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 (THz) compressive imaging can obtain two dimensional image with a single or linear detector, which can overcome the bottleneck problem of lacking of THz two dimensional detectors. In this presentation, we propose a method to obtain two dimensional images using a linear detector. A plano-convex cylindrical lens is employed to perform Fourier transform and to encode one dimensional information of an object into wavelengths. After recording, both amplitude and phase information for different frequency at each pixel of the line detector are extracted, two dimensional image of the object can be reconstructed. Numerical simulation demonstrates the validity of the proposed method.
Focusing of terahertz (THz) surface plasmon polaritons (SPPs) excited by linearly and circularly polarized THz radiation is investigated experimentally and theoretically. A high-speed THz-SPPs imaging system is built up to measure both the amplitude and phase of the excited THz-SPPs. For the horizontally polarized THz radiation, the THz-SPPs will be focused in the centre of the semicircular slit and the phase images reveals a π/2 Gouy phase shift though the focal spot of THz-SPPs. With the illumination of vertically polarized THz radiation, the focal spot in the centre will split into two focal spots in the y-direction. For the circularly polarized incident THz radiation, the focal spot of THz-SPPs will shift upward or downward in the y-direction. FDTD simulations are performed and compared with the experimental results. A good agreement between experimental results and simulation results can be found.
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.
We present a novel technology to dynamically control the wave front of the terahertz (THz) beam with photo-generated
carriers. The computer generated hologram is projected onto a silicon wafer by a conventional optical spatial light
modulator. The photo-generated carriers on the silicon surface will from a hologram to modulate the wave front of the
input THz beam. Some special field distributions and vortex beams are generated using this method. This technology is
broadband, structure free, tunable, and all-optical controllable. It will provide numerous possible applications in future
THz imaging and communication systems.
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.
Terahertz wave (THz, also name T-Ray) belongs to far-infrared electromagnetic radiation. Since its unique properties,
THz techniques have been paid more and more attentions during the past decades. In this field, THz digital holography is
an important research branch, which can accurately extract three-dimensional optical information of objects. Based on
features of this technique, it greatly reduces the experimental time and clearly presents the diffraction phenomena of the
transmitted THz waves. We elucidated our works about the THz digital holography in recent years. Some key techniques
in the THz digital holography are selected as research objects, which are the reflection measurement, quasi-near-field
measurement, balanced electro-optic (EO) imaging, and polarization detection. From these four aspects, including the
measurement mode, improvement of the spatial resolution, optimization of the signal to noise ratio (SNR), and
acquirement of the polarization information, the THz digital holography imaging system has been investigated
experimentally and theoretically. These works enhance the performances of the system and promote the practicability of
the THz digital holography. Although there are a lot of theoretical and technical difficulties to be overcome in the
practical applications, it is firmly believed that the THz digital holography will present strong abilities in factory and
research fields in the future.
The polarization information of various ores and gems in the terahertz (THz) frequency region has been investigated.
The images of the samples for different polarization are captured by a balanced polarization imaging system. The system
employs a balanced electro-optic (EO) detection method for two-dimensional THz real-time imaging, which
systemically integrates the THz balanced EO sampling technique and the dynamic subtraction technique. The proposed
method can effectively improve the signal to noise ratio and the spectrum measurement accuracy of the imaging system.
The imaging speed is dramatically reduced by using two high speed CCDs which are used to detect two orthogonal
polarization components of probe beam. The subtraction of two corresponding images presents the balanced image of the
sample. By rotating the polarization of the probe beam by 45 degree, another polarization component which is
orthogonal to the present one can be measured. The experiment results demonstrate the advantage of the method. The
spectra of the samples on each point can be extracted from a series of images, thus the refractive indices, absorption
coefficients, and polarization rotation coefficient can be drawn. The information can be used to identify samples.
Continues wave terahertz imaging has been used widely in the field of security inspection and nondestructive
examination because of its simplicity and stability. In this presentation, we proposed an image method with continues
wave terahertz interferometry to obtain the sample's phase information. In the experiment, a reference terahertz beam
was added into the exiting continues wave terahertz imaging system to be a Michelson interferometer. With three maps
obtained at three fixed phase-shift positions, a phase image is obtained by using a phase shift algorithm. Afterwards, this
phase image is unwrapped to get its accurate phase profile. By this method, a bulk of foam with two height steps
structure is imaged. The result shows that the inner structures of samples can be identified clearly and the relative optical
depth profiles of samples can be obtained.