A photonic crystal fiber (PCF) sensor is proposed for the detection of refractive index (RI), magnetic field intensity, and temperature. The large air hole in the center of the sensor is filled with a magnetic fluid (water-based Fe3O4) whose RI changes with the intensity of the magnetic field and temperature. The top of the sensor is polished and coated with gold film, and external sensing technology is used to detect changes in the RI of the analyte. Due to the characteristics of the structure, the lower and upper parts of the sensor can detect magnetic field intensity, temperature, and RI. The simulation results show that the proposed magnetic field, temperature, and RI sensitivities of the sensor can reach the maximum of 1.57 nm/Oe, −1 nm / ° C, and 7600 nm/RIU in the detection range of 22 to 250 Oe, 8°C to 60°C, and 1.38 to 1.42 RIs, respectively. The proposed multiparameter PCF plasmonic sensor can be used for hyperthermia monitoring, medical and chemical sample analysis, biomolecular engineering, and magnetocardiography.
Cascaded optical parametric oscillations generating a tunable terahertz (THz) wave are analyzed to solve the problem of low quantum conversion efficiency in a THz-wave parametric oscillator. The forward and backward optical parametric processes are theoretically analyzed based on periodically poled lithium niobate (PPLN) as an example. Tuning characteristics of the THz wave that relate to the parameters of the pump wavelength, the grating period of PPLN, and the working temperature are numerically simulated. The gain and absorption characteristics of the generating THz wave are deduced in the situation of quasiphase-matching configuration at different working temperatures.
A surface plasmon resonance biosensor based on three-hole photonic crystal fiber (PCF) is analyzed by the finite element method. The results demonstrate that the biosensor will exhibit different loss spectra characteristics under the conditions of nonuniform thicknesses of the auxiliary dielectric layer, the gold layer, and the biolayer in the three-hole PCF, respectively. Furthermore, the sensing properties in both areas of resonant wavelength and intensity detection are discussed. Numerical results show excellent sensing characteristics when the thickness of the auxiliary dielectric layer is s=1 μm and the gold d gold =40 nm , respectively. The sensor resolution of the biolayer thickness is demonstrated more than 0.05 nm in the vicinity of 0.6 μm with the amplitude-based method.
A high-powered pulsed terahertz (THz)-wave has been parametrically generated via a surface-emitted THz-wave parametric oscillator (TPO). The effective parametric gain length under the noncollinear phase matching condition was calculated for optimization of the parameters of the TPO. A large volume crystal of MgO:LiNbO3 was used as the gain medium. THz-wave radiation covering a frequency range from 0.87 to 2.73 THz was obtained. The average power of the THz-wave was 9.12 μW at 1.75 THz when the pump energy was 94 mJ, corresponding to an energy conversion efficiency of about 9.7×10−6 and a photon conversion efficiency of about 0.156%. The THz-wave power in our experiments is high enough for practical applications to spectrum analysis and imaging.
Low-resolution of terahertz (THz) imaging troubled its applications in the field of medical diagnosis
and security inspection. The continuous wave (CW) THz imaging system utilizing a pyroelectric
detector has been realized. The two crucial factors were analyzed in theory and verified in experiment;
a high-quality THz image with the resolution of 0.4mm was obtained by choosing suitable imaging
parameters. In our experiment the THz wave frequency of 2.53 THz, the spot size of 1.8 mm and the
step length of 250 μm were selected to achieve high quality THz image. We also image several samples
with different materials utilizing this system, and the results were very good.
High-power nanosecond pulsed THz-wave radiation was achieved via a surface-emitted THz-wave parametric oscillator
(TPO). The effective parametric gain length under the condition of noncollinear phase matching was calculated to
optimize the parameters of the TPO. Only one MgO:LiNbO3 crystal with large volume was used as gain medium.
THz-wave radiation from 0.8 to 2.9 THz was obtained. The maximum THz-wave output was 289.9 nJ/pulse at 1.94 THz
when pump power density was 211 MW/cm2, corresponding to the energy conversion efficiency of 3.43×10-6 and the
photon conversion efficiency of about 0.05%. The far-field divergence angle of THz-wave radiation was 0.0204 rad at
vertical direction and 0.0068 rad at horizontal direction.
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