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.
Terahertz ray, as a new style optic source, usually means the electromagnetic whose frequencies lies
in between 0.1THz~10THz, the waveband region of the electromagnetic spectrum lies in the gap between microwaves and
infrared ray. With the development of laser techniques, quantum trap techniques and compound semiconductor techniques,
many new terahertz techniques have been pioneered, motivated in part by the vast range of possible applications for
terahertz imaging, sensing, and spectroscopy. THz imaging technique was introduced, and THz imaging can give us not
only the density picture but also the phase information within frequency domain. Consequently, images of suspicious
objects such as concealed metallic or metal weapons are much sharper and more readily identified when imaged with
THz imaging scanners. On the base of these, the application of THz imaging in nondestructive examination, more
concretely in large scale circuit failure inspection was illuminated, and the important techniques of this application were
introduced, also future prospects were discussed. With the development of correlative technology of THz, we can draw a
conclusion that THz imaging technology will have nice application foreground.
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.
A design of light modulator for THz amplitude and phase modulations has been presented in this paper.
Simplest versus of the Drude model is adopted, in which the collision damping is independent of the carrier
energy. In our experiment, we use THz-TDS as THz source and detector. A laser whose wavelength is
808nm was used to irradiate the intrinsic Si(high-resistance), so as to let it generate the Photo-carriers ,and
to influence the conductance . The Photo-carriers will change the absorption coefficient of the THz wave
and also influence the dielectric of the sample, hence to control the characteristics of the THz wave in the
silicon . By changing the light intensity , due to the different photon-generated carrier concentration ,the
single transmission of the THz wave in the silicon wafer sample is changing remarkable . Theoretically,
the modulation depth can be more than 80%. we present our design of light modulator for THz, and show
the Digital simulation of our design. Also, according to this design theory, Optical/electronic integrated
modulation of THz can be realized, that will be our future work.
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