On-chip high-sensitivity photonic temperature sensor based on a GaAs microresonator.

We demonstrate an on-chip high-sensitivity photonic temperature sensor based on a GaAs microdisk resonator. Based on the large thermo-optic coefficient of GaAs, a temperature sensitivity of 0.142 nm/K with a measurement resolution of 10 mK and low input optical power of only 0.5 µW was achieved. It exhibits great potential for chip-scale biological research and integrated photonic signal processing.

Ultrafast Resolution-Enhanced Digital Optical Frequency Comb-Based BOTDA with Pump Pulse Array Coding.

In this letter, a resolution enhancement and signal-to-noise ratio (SNR) improvement scheme for digital optical frequency comb (DOFC)-based Brillouin optical time-domain analysis (BOTDA) ultrafast distributed sensing employing a pump pulse array is proposed. Based on the properties of the time-invariant linear system and the cyclic revolution theorem, experimental results indicate that its spatial resolution reaches 10.24 m while the frequency uncertainty is below 2 MHz over a 9.5 km fiber. Moreover, the response time is only 209.6 µs and the temperature measurement error is less than 0.52 °C.

Optical, mechanical and thermal characterizations of suspended chalcogenide glass microdisk membrane.

As a promising infrared optical material, the physical characteristics of patterned chalcogenide glass (ChG) membranes are of great importance for the improvement of device performances. In this work, based on the suspended membrane configuration, we have demonstrated the mechanical and thermal characterizations of the Ge11.5As24Se64.5 ChG optical microdisk resonator. By approximation of ChG cantilever configuration, the out-of-plane minimum mechanical strength of the microdisk membrane was measured to be 150 MPa by exploiting atom force microscope (AFM). This value is two orders of magnitude smaller than that of the bulk material, which is beneficial to achieve better mechanical compliance in terms of the ChG membrane sensors. To illustrate the effect of environmental temperature variation on the optical response of the ChG microdisk membrane with quality factor (Q-factor) of 2.87 × 104, the thermal drift was characterized to be 90.2 pm/°C by changing the substrate temperature from 30 °C to 44 °C. The characterization of multi-parameters in combination with the ChG free-standing microdisk prototype is conducive to further expand the potentials of ChG membrane in the ultrasound and other cavity optomechanical sensing.

Silica-microsphere-cavity-based microwave photonic notch filter with ultra-narrow bandwidth and high peak rejection.

We propose and experimentally demonstrate a microwave photonic (MWP) notch filter based on a silica microsphere cavity. By using a high-Q-factor (∼1e7) cavity with a diameter of 132 um, the filter bandwidth can be easily decreased to 15 MHz in terms of simple fabrication and flexible coupling. Then we use the advanced modulation technique based on a dual parallel Mach-Zehnder modulator to further improve peak rejection (PR). The experimental results show that the MWP notch filter with its PR beyond 55 dB and frequency tunability range over 8 GHz has been achieved in combination with double-sideband modulation. To the best of our knowledge, this is a record for PR and bandwidth considered simultaneously for an MWP filter based on silica microcavities. Thus, the proposed MWP filter will be useful in the fields of microwave photonic signal processing, radar systems, etc.

Spatial resolution improvement of single-shot digital optical frequency comb-based Brillouin optical time domain analysis utilizing multiple pump pulses.

A spatial resolution improvement scheme for the digital optical frequency comb (DOFC)-based single-shot Brillouin optical time domain analysis (BOTDA) by utilizing multiple pump pulses is demonstrated. Assisted by four pump pulses, the spatial resolution can be improved by four times without decreasing the detection resolution. The response time, and the spatial resolution of our scheme over 10 km fiber, are 0.1 ms and 12.5 m. Distributed temperature and strain measurements are carried out with detection resolutions of 1.6°C and 44 µÏµ, respectively, and the capability of dynamic measurement of this proposed BOTDA is also demonstrated by probing a vibration with frequency up to 1.2 kHz.

Parallel interrogation of the chalcogenide-based micro-ring sensor array for photoacoustic tomography.

Photoacoustic tomography (PAT), also known as optoacoustic tomography, is an attractive imaging modality that provides optical contrast with acoustic resolutions. Recent progress in the applications of PAT largely relies on the development and employment of ultrasound sensor arrays with many elements. Although on-chip optical ultrasound sensors have been demonstrated with high sensitivity, large bandwidth, and small size, PAT with on-chip optical ultrasound sensor arrays is rarely reported. In this work, we demonstrate PAT with a chalcogenide-based micro-ring sensor array containing 15 elements, while each element supports a bandwidth of 175 MHz (-6 dB) and a noise-equivalent pressure of 2.2 mPaHz-1/2. Moreover, by synthesizing a digital optical frequency comb (DOFC), we further develop an effective means of parallel interrogation to this sensor array. As a proof of concept, parallel interrogation with only one light source and one photoreceiver is demonstrated for PAT with this sensor array, providing images of fast-moving objects, leaf veins, and live zebrafish. The superior performance of the chalcogenide-based micro-ring sensor array and the effectiveness of the DOFC-enabled parallel interrogation offer great prospects for advancing applications in PAT.

Simultaneous determination of gross alpha/beta activities in water by liquid scintillation counting and its applications in the environmental monitoring.

Based on the standards of ISO11704-2018 and ASTM D7283-17, a method for simultaneous determination of gross alpha and gross beta activity concentrations in water by liquid scintillation counting (LSC) was established, which can be applied to various types of water samples in routine monitoring, such as drinking water, groundwater, geothermal water, seawater, and radioactive wastewater. The sample's pH value and concentrated volume must be controlled to avoid quenching as much as possible. The validation tests show that the deviations of gross alpha and gross beta activities can satisfy quality control requirements in a wide range of activity ratios from 1:102 to 67:1. For the actual samples, the measurement results of the LSC method are in good agreement with those of the thick source method, in which the relative deviations of gross alpha and gross beta are both less than 15% for these two methods. Moreover, the LSC method performs better in detection limit and has a simpler pretreatment process than the thick source method.

High-speed single-exposure time-reversed ultrasonically encoded optical focusing against dynamic scattering.

Focusing light deep inside live scattering tissue promises to revolutionize biophotonics by enabling deep tissue noninvasive optical imaging, manipulation, and therapy. By combining with guide stars, wavefront shaping is emerging as a powerful tool to make scattering media optically transparent. However, for in vivo biomedical applications, the speeds of existing techniques are still too slow to accommodate the fast speckle decorrelation of live tissue. To address this key bottleneck, we develop a quaternary phase encoding scheme to enable single-exposure time-reversed ultrasonically encode optical focusing with full-phase modulations. Specifically, we focus light inside dynamic scattering media with an average mode time down to 29 ns, which indicates that more than 104 effective spatial modes can be controlled within 1 millisecond. With this technique, we demonstrate in vivo light focusing in between a highly opaque adult zebrafish of 5.1 millimeters in thickness and a ground glass diffuser. Our work presents an important step toward in vivo deep tissue applications of wavefront shaping.

Highly efficient acousto-optic modulation using nonsuspended thin-film lithium niobate-chalcogenide hybrid waveguides.

A highly efficient on-chip acousto-optic modulator is as a key component and occupies an exceptional position in microwave-to-optical conversion. Homogeneous thin-film lithium niobate is preferentially employed to build the suspended configuration for the acoustic resonant cavity, with the aim of improving the modulation efficiency of the device. However, the limited cavity length and complex fabrication recipe of the suspended prototype restrain further breakthroughs in modulation efficiency and impose challenges for waveguide fabrication. In this work, based on a nonsuspended thin-film lithium niobate-chalcogenide glass hybrid Mach-Zehnder interferometer waveguide platform, we propose and demonstrate a built-in push-pull acousto-optic modulator with a half-wave-voltage-length product VπL as low as 0.03 V cm that presents a modulation efficiency comparable to that of a state-of-the-art suspended counterpart. A microwave modulation link is demonstrated using our developed built-in push-pull acousto-optic modulator, which has the advantage of low power consumption. The nontrivial acousto-optic modulation performance benefits from the superior photoelastic property of the chalcogenide membrane and the completely bidirectional participation of the antisymmetric Rayleigh surface acoustic wave mode excited by the impedance-matched interdigital transducer, overcoming the issue of low modulation efficiency induced by the incoordinate energy attenuation of acoustic waves applied to the Mach-Zehnder interferometer with two arms in traditional push-pull acousto-optic modulators.

Stack releases of radionuclides from an integrated steel plant in China.

Crude steel production in China made up the majority of the global output, at 49.5% in 2014. High temperature smelting processes result in the release of natural radionuclides, including radon gas and other air pollutants into the atmosphere. This paper conducts an analysis of the raw materials, end products and flue gas sampled from an integrated steel plant from within China's Jiangxi Province, with annual production of 8.50 Mt of crude steel. Normalized stack emissions factors of radionuclides from steel production were first reported in China. The results showed that sintering was the main process that released natural radionuclides, and the main radionuclides released into the atmosphere were 222Rn (86.4 GBq/Mt), 210Pb (13.4 GBq/Mt), and 210Po (1.71 GBq/Mt). The results provided essential basic data for radiological impact assessment of steel production, as well as that of nuclear energy chain, coal chain and other electricity sources.

Fresnel-reflection-based fiber sensor for high-temperature measurement.

A fiber sensor system was developed to measure high temperatures. The system consists of a diode laser as the light source, three optical couplers, two sensing fiber ends, and two photodetectors. The measurement is based on the relative Fresnel reflection intensity and the thermo-optic effect of the fiber. The application of this relative technique can operatively eliminate the errors resulting from light source fluctuations and the effect of the environment. The stability of the system for long-duration measurements can also be effectively improved.