Zhenfeng Gong

Compact surface plasmon resonance imaging sensing system based on general optoelectronic components

We present a simple surface plasmon resonance imaging (SPRi) sensing system based on some common optoelectronic devices in this paper. Using an optical fiber based SPR sensor as sensing element in our system, the SPRi system is dramatically compact. A small universal LED is used as the light source. The light intensity is record as images that can be captured by a simple web camera. A Microsoft Visual C++6.0 based Windows software program is written to process the image data which contain SPRi information. Experimental results show that the relationship between the relative intensity and RI is a linear relation in a RI range from 1.3396 to 1.3645. Using this SPRi device, we measure the specific binding between the Con A and RNase B, which demonstrates its capability for biomedical selective affinity monitoring. The proposed SPRi sensing system also has the capacity for biochemical multiple channel measurement with further investigation.

Miniature Fiber-Optic Strain Sensor Based on a Hybrid Interferometric Structure

We present a compact fiber-optic strain sensor with a hybrid interferometric structure, including a micro-cavity Fabry-Pérot interferometer (MC-FPI) and a Mach-Zehnder interferometer (MZI). The sensor is formed by splicing two conventional single-mode fibers (SMFs), one as the lead-in fiber and the other as the lead-out fiber, to both ends of a photonic crystal fiber (PCF). Through controlling the splicing parameters, the lead-in SMF/PCF splice forms a micro-cavity and causes the collapse of the microholes in the PCF, which acts as a mode splitter/combiner. For the lead-out SMF/PCF splice, no micro-cavity is formed and the splicing point only functions as a mode splitter and combiner. The PCF together with the two splicing points form the MZI. Sensor prototypes with different MC-FPI lengths are developed. Combining reflection and transmission spectra together, the sensor achieves a high strain sensitivity, which can find application in real strain measurement.

Fiber-Optic Anemometer Based on Distributed Bragg Reflector Fiber Laser Technology

We present a novel fiber-optic anemometer based on a distributed Bragg reflector (DBR) fiber laser. The anemometer consists of a fiber laser pressure sensing element and a Venturi tube designed to convert the wind velocity into differential gas pressure that can be measured by the fiber-laser sensor. A DBR fiber laser that has two polarization modes is designed and fabricated as the major sensing element in this anemometer. The fiber-laser sensor is demodulated by the beat frequency of the two polarization modes, which has higher sensitivity and lower cost over wavelength-demodulated fiber-laser sensors. The experimental results show that the sensors response to wind velocity is quadratic in the measurement range of 8 ~ 40 m/s, the short term repeatability is better than 0.5%, and its sensitivity is impacted by the power of pump laser. Additionally, this anemometer has the potential capability to be used as a flow meter for both gas and liquid flows.

Fiber Optic Liquid Level Sensor Based on Integration of Lever Principle and Optical Interferometry

We present a fiber-optic liquid level sensor that is conducted by a combination of optical interferometry and lever principle. The sensing unit is a Mach-Zehnder interferometer (MZI), which is formed by sandwiching a piece of photonic crystal fiber (PCF) between two single-mode fibers (SMFs). The measuring equipment is composed of a rotatable lever and a fixed link. The rotatable lever includes two different length arms, i.e., L1 and L2. Both ends of the MZI are glued on the tip of the L2 arm and the fixed link using ethoxyline, respectively. A hanging stick, which is dipped into a liquid tank, is directly mounted on the other end of the rotatable lever. The buoyancy will increase as the stick depth of immersion into the liquid increases. The tension the MZI subjected will increase according to the proportion of L1/L2 on account of the lever principle. The sensitivity of the sensor could be regulated with different ratios of lever arms. In our experiment, a maximum sensitivity of 111.27 pm/mm was obtained with a 1 : 7.8 ratio of two lever arms L1/L2. The demonstrated liquid level sensor has the advantages of simple structure, easy fabrication, low cost, and high sensitivity.

Fiber Ring Laser-Based Displacement Sensor

We reported an erbium-doped fiber ring laser (FRL) displacement sensor based on a single-mode fiber (SMF) loop tied into the laser cavity. The proposed fiber loop structure acts as the sensing head as well as the filter of the FRL. A good linear relationship is obtained both in principle and in experiments between the displacement of one end of the loop and the central wavelength of the proposed FRL. The average sensitivity of this sensor reaches 227.5 pm/mm in the displacement range of 0–30 mm. High optical signal-to-noise ratio (

Loss analysis of physical contact fiber-optic connector induced by the endface geometry and the contact force

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Research on fiber-optic cantilever-enhanced photoacoustic spectroscopy for trace gas detection

dB) and narrow 3-dB bandwidth (<0.7 nm) are also achieved due to the FRL structure. Moreover, the macrofiber loop, as the key sensor head of the proposed sensing system, is tied with simple SMF without removing the coating, which has obvious advantages of firm structure with a wide range of displacement measurement and easy fabrication with low-cost SMF.

Parylene-C diaphragm-based fiber-optic Fabry-Perot acoustic sensor for trace gas detection

Abstract. Optical loss of fiber-optic connectors has a vital impact on fiber-optic-related systems. We analyze the contact loss caused by the endface geometry and the contact force. Based on analytical and simulated results, the analytical equations of the insertion loss (IL) and return loss (RL) as a function of the endface geometry and the contact force are derived. Then four fiber-optic connectors are experimentally tested. The experimental results are well consistent with the theoretical results, which show that there is an optimum relationship between the endface geometry and the contact force to ensure a low IL and a high RL.

Glycoprotein Detection by Using the Surface Plasmon Resonance Technology

We demonstrate a new scheme of cantilever-enhanced photoacoustic spectroscopy, combining a sensitivity-improved fiber-optic cantilever acoustic sensor with a tunable high-power fiber laser, for trace gas detection. The Fabry-Perot interferometer based cantilever acoustic sensor has advantages such as high sensitivity, small size, easy to install and immune to electromagnetic. Tunable erbium-doped fiber ring laser with an erbium-doped fiber amplifier is used as the light source for acoustic excitation. In order to improve the sensitivity for photoacoustic signal detection, a first-order longitudinal resonant photoacoustic cell with the resonant frequency of 1624 Hz and a large size cantilever with the first resonant frequency of 1687 Hz are designed. The size of the cantilever is 2.1 mm×1 mm, and the thickness is 10 μm. With the wavelength modulation spectrum and second-harmonic detection methods, trace ammonia (NH3) has been measured. The gas detection limits (signal-to-noise ratio = 1) near the wavelength of 1522.5 nm is achieved to be 3 ppb.

Inline fiber interference-based refractive-index sensor

We demonstrate a high-sensitivity fiber-optic Fabry-Perot acoustic sensor based on a thin Parylene-C diaphragm. The vacuum thermal evaporation deposition method is used to fabricate the Parylene-C nanofilm, which possesses strong adhesion and good compactness. Based on these characteristics, the Parylene-C diaphragm is fabricated with 9 mm in diameter and 500 nm in thickness. The noise limited equivalent acoustic signal level is 33.5 μPa/Hz1/2 at the frequency of 30 Hz. The pressure sensitivities of the acoustic sensor are more than 1000 mV/Pa at the frequency from 10 Hz to 30 Hz. The fundamental resonance frequency of the Parylene-C diaphragm is about 13 Hz. The acoustic sensor is applied in a multiple trace gas detection system based on photoacoustic spectroscopy. The detection limits of acetylene (C2H2), carbon monoxide (CO) and carbon dioxide (CO2) are achieved to be 0.25, 0.32 and 1.1 parts-per-million, respectively.