Micro/nano-structured amorphous carbon promises functional prospects in energy-saving, water purification, nonlinear optics, catalysis, sensors, and the internet of things, but there exist many challenges, especially in rapid synthesized nanostructured carbon materials towards performance improvement. Thereby, a transfer-free digital photochemical synthesis method is studied here via scalable single-step nanosecond laser processing. Controllable photon energy from a 1064nm wavelength nanosecond laser drives different degrees of carbonization on paper surfaces. The blended cellulose-lignin network is converted into a series of micro/nano-stacked porous carbon materials during fabrication. High-resolution transmission electron microscope showcases that lattice characteristics of synthesized carbon shift according to optical parameters. A comparison of material morphologies formed at different conditions can be found here. Nanosecond laser processing opens a new avenue for the rapid preparation of carbon nanomaterials on paper substrates with special textures and special microstructures, promising more carbon-based multifunctional devices.
An enhanced laser self-mixing Doppler velocimeter by fiber Bragg grating (FBG) is proposed. In fiber sensing, FBG is often used as an optical filter to select the wavelength of the light using the narrow reflection spectrum. The Doppler frequency shift from the rotating target can be parsed in the self-mixing interferometry (SMI) signal. The frequency-fluctuant self-mixing signal is transformed into intensity variations by a FBG when the laser wavelength is set to the edge of the FBG steep transmission profile. An experimental comparison between the enhanced and the traditional SMI approaches is made. The magnitude of obtained FBG-enhanced SMI signal is about 40 times stronger than that from traditional SMI. The result of the experiments indicates that enhanced self-mixing Doppler velocimetry by FBG can be applied to velocity sensing. This method has potential application in the engineering industry because the FBG is easy to fabricate and connect to a SMI system and the wavelength of FBG can be changed to match the different lasers for an enhanced SMI signal.
A fiber-optic micro-electromechanical systems (MEMS) extrinsic Fabry-Perot interferometer (EFPI) pressure sensor exploiting microwave photonics filtering technique is firstly proposed and experimentally demonstrated. A single-bandpass microwave photonic filter (MPF) which mainly consists of a spectrum-sliced light source, a pressurized EFPI, a phase modulator (PM) and a length of dispersion compensating fiber (DCF) is demonstrated. The frequency response of the filter with respect to the pressure is studied. By detecting the resonance frequency shifts of the MPF, the pressure can be determined. The theoretical and experimental results show that the proposed EFPI pressure sensor has a higher resolution and higher speed than traditional methods based on optical spectrum analysis. The sensitivity of the sensor is measured to be as high as 86 MHz/MPa in the range of 0-4MPa.
By combining self-mixing interferometer (SMI) and grating interferometer (GI), a self-mixing grating interferometer (SMGI)
is proposed in this paper. Self-mixing interference occurs when light emitted from a laser diode is diffracted by the doublediffraction
system and re-enters the laser active cavity, thus generating a modulation of both the amplitude and the frequency
of the lasing field. Theoretical analysis and experimental observations show that the SMGI has the same phase sensitivity as
that of the conventional GI and the direction of the phase movement can be obtained from inclination of the interference
signal. Compared with the traditional SMI, the phase change of interference signal in SMGI is independent of laser
wavelength, providing better immunity against environmental disturbances such as temperature, pressure, and humidity
variation. Compared with the traditional GI, the SMGI provides a potential displacement sensor with directional
discrimination and quite compact configuration.
An advanced sinusoidal phase-shifting technique and a time-domain phase demodulation method were used to improve the measurement accuracy and realize the real-time measurement speed of the laser self-mixing interferometer in a large range of displacement. An electro-optic crystal modulator (EOM) was used to realize the sinusoidal phase-shifting on the laser beam in the external cavity. The interference signal was demodulated using a time-domain phase demodulation method. The speed requirement could be met by combining the two together in a wide range of displacement measurement processes together with the real-time measurement requirement as an interferometer at the same time. It was experimentally verified that the displacement measurement precision of a sinusoidal phase-shifting laser self-mixing interferometer could reach less than 0.5 μm in the hundred mm large-scale displacement measuring process. In addition, the factors affecting the interferometer’s measurement speed in the real-time displacement measurement process is analyzed and the maximum speed of our system was obtained as well. Keywords: self-mixing interference; phase modulation; time-domain phase demodulation
We propose a simple optical fiber current sensors based on the Lorentz force to measure the current. We use two copper carrying wires, and the two carrying wires are parallel fixed to the insulated coil spring. Then, the two optical fibers are vertically fixed on two copper, respectively. When the current input the wires, Loren magnetic force will be existed between wires. The force causes deformation of the spring and leads to the displacement of the fiber’s end faces. So the spectra should be changed. The experimental device is used to measure the current at range for the 1-5 A, the response time is about 0.1 seconds, and resolution sensitivity of the sensor is 10 nm/A. The results show that the device is simple and low costs. It has a potential applied in high current sensing.
The Self-Mixing Interference (SMI) effect of a Vertical-Cavity Surface-Emitting Laser (VCSEL) is studied in this paper.
The analysis and experiment are presented to verify the dynamics of the VCSEL. The phenomenon is observed and
contrasted with traditional interference phenomenon. The output property of VCSEL is modulated by the change of
cavity length and feedback intensity. An interferometer using VCSEL self-mixing based on temporal carrier phase
shifting technique is studied. Theoretical analysis and simulation calculations are presented and some errors of this
method are discussed.
A new self-mixing interferometer (SMI) based on temporal carrier phase shifting technique is presented. Self-mixing
interference occurs in the laser cavity by reflecting the light from a mirror-like target in front of the laser. Triangular
phase modulation of the beam is obtained by an electrooptic modulator (EOM) in the external cavity. The phase of SMI
signal coming from the photodetector is extracted by the phase shift demodulation algorithm based on sampling
technique. Theoretical analysis and simulation calculations are presented and some errors of this method are discussed.
The interferometer is applied to measure the Micro-vibration of a high-precision commercial PZT with an accuracy of
<10nm.
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