A sensitive, real-time seven core optical fiber based Mach-Zehnder interferometer (MZI) sensor for liquid refractive index detection is proposed, fabricated and characterized. A trapezoid body with an inverted wedge shape groove in the center is used to design the MZI. The two ends of the trapezoid body play the roles of micro-prisms, and the middle parts of the trapezoid body and the groove play the roles of reference and sensing arms. A series of performance tests were carried out by immersing the sensor in different kinds of solutions to verify the universal applicability of the sensor. The MZI sensor is as small as only 43 μm × 8 μm, and at the same time with sensitivity of 1616 nm/RIU. Nominally, we realized a completely integrated optical sensing system. And, this system actually could be the building block of more powerful integrated chemical sensing chip for health, security and industry application.
Terahertz spectra modulation can be potentially used in the remote sensing. The spectra modulation of terahertz radiation from two plasmas is demonstrated experimentally. With the comparison of the spectra of terahertz radiated from single and two plasmas, the output spectrum of terahertz wave has been proved to be of interference superposition of the two separate terahertz waves. With measurement and analysis of the polarization states of the output terahertz wave, it is fund that the two orthogonal components of THz electric fields have effects on the components involved in the interference of two terahertz waves. The output terahertz radiation from two plasmas is simulated, and the result shows that the distance between two plasmas contributes greatly to the spectrum modulation of terahertz radiation.
Pulsed terahertz reflected imaging technology has been expected to have great potential for the non-invasive analysis of artworks. In this paper, three types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by a pulsed terahertz reflected imaging system. These preset defects include a circular groove, a cross-shaped slit and a piece of “Y-type” metal plate built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. Additionally, three-dimensional analyses have been performed in order to reveal the internal structure of defects. Terahertz reflective imaging can be applied to the defect investigation of the murals.
Terahertz time-domain spectroscopy (THz-TDS) imaging technology has been proposed to be used in the non-invasive detection of murals. THz-TDS images provide structural data of the sample that cannot be obtained with other complementary techniques. In this paper, two types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by the terahertz reflected time domain spectroscopy imaging system. These preset defects include a leaf slice and a slit built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. With this THz tomography, different defects with the changes of optical thickness and their relative refractive index have been identified. The application of reflective pulsed terahertz imaging has been extended to the defect detection of the murals.
Terahertz (THz) radiation is an under developing range in the electromagnetic spectrum. It has attracted a lot of
attentions due to its various potential applications. However, THz systems are difficult to be integrated into a smart size
due to the limitation of its long wavelength. In this presentation, we propose a new approach to design planar lenses with
a thickness of several hundred nanometers in the THz range. The fabricated lenses are characterized with a focal plane
imaging system and it is found that they can focus the THz light and image an object well. It is expected that this new
approach can pave a way for smart THz systems integration.
An optical refractive index sensor based on the Rayleigh anomaly of the gold grating is demonstrated in the terahertz (THz) wave band. A pronounced peak due to the Rayleigh anomaly of the gold grating is observed in the reflection spectrum, the center wavelength of which is sensitive to the environmental refractive index on the top of the grating. The wavelength of the Rayleigh anomaly reflection peak and the corresponding sensitivity are solely determined by the period of the gold grating, the larger the period, the longer the resonance wavelength and the higher the sensitivity. Therefore, a higher sensitivity can be achieved in the THz wave band. Both theoretical and experimental investigations show that the shape and intensity of the Rayleigh anomaly reflection peaks are determined by the duty cycle of the grating, for the value of the duty cycle about 0.4, the maximum intensity of the Rayleigh anomaly reflection peak was achieved.