The passive terahertz imaging human body security technology has begun to be applied in dense pedestrian flow security fields such as subways and public venues. However, passive terahertz imaging systems directly generate terahertz images, which have problems such as low signal-to-noise ratio and poor resolution. For the identification of suspicious objects hidden under human clothing, the naked eye observation method by security personnel is difficult to distinguish suspicious objects, with a high error rate and slow speed. To balance the accuracy and speed of detecting suspicious objects hidden under human clothing in security scenarios, taking into account terahertz image quality and target detection accuracy, a DeepLabV3+ deep learning model is used to detect targets, achieving object detection and recognition based on passive terahertz imaging human security systems.
Due to the capability of achieving versatile control of differently polarized electromagnetic waves, anisotropic metasurfaces have attracted extensive attentions. To manipulate terahertz waves flexibly, we propose a tunable anisotropic metasurface based on phase change material vanadium dioxide (VO2). It is composed of a gold bottom layer deposited on the back of polyimide dielectric layer and a gold patch located on the front of the polyimide dielectric substrate. When VO2 is in the insulating state, the predesigned metasurface produces diversified functions, including terahertz beam splitting, deviation focusing, and multivortex beam under different polarization terahertz wave incidence. When VO2 becomes a metallic state, the proposed metasurface changes the number of terahertz beams, the shape of vortex beams, and the focusing effect. This scheme provides an innovative idea for the dynamic regulation of the terahertz wave in future terahertz technology systems.
Digital coded metasurface has greatly simplified the method for electromagnetic wave regulation. However, the traditional metasurface usually focuses on the half-space beam modulation, such as transmissive or reflective direction regulation, which hinders the application of the metasurface-based device. We proposed a full-space terahertz regulation metasurface, which can realize the functions of beam splitting, vortex beam convolution, and focusing for both transmissive and reflective modes. Furthermore, the transmission and reflection modes can be easily switched by changing the external temperature of vanadium dioxide. The presented structure shows excellent performance of full-space terahertz regulation. This method provides a new idea for multifunctional terahertz devices and can be exploited in applications where active manipulation of terahertz transmission direction is required.
A bi-function switchable metasurface structure is proposed to realize dynamic switch function between ultrabroadband terahertz absorber and polarization converter. The structure consists of a SO2 hemisphere in a square lattice, two different radius hybrid gold-photosensitive silicon rings cladding configuration, and metal substrate. When the conductivity of the photosensitive silicon is 1.0 × 104 S / m (i.e., in the metallic state), the metasurface structure exhibits ultrabroadband terahertz absorber with above 90% absorption in the range of 3.96 to 10.0 THz. The high absorption performance can be maintained before incident angle of 50 deg. When the conductivity of the photosensitive silicon is 2.5 × 10 − 4 S / m (in the dielectric state), the proposed structure serves as a terahertz polarization converter. The polarization conversion rate (PCR) is larger than 90% from 3.88 to 7.21 THz within the incident angle range of 0 deg to 80 deg. By changing the conductivity of the photosensitive silicon, absorbance and PCR can be dynamically adjusted. The scheme provides a new perspective to explore multifunction terahertz device.
We present an ultra-compact gate-voltage-controlled terahertz power divider based on graphene plasmonic waveguide,
which consists of five graphene ribbons embedded in the polymethylmethacrylate (PMMA) substrate. We have
theoretically explained their mechanisms as bias voltage change induced carrier density of graphene modification and the
coupling coefficients of graphene plasmon effect after carrier density change, respectively. The surface plasmonic
polariton (SPP) propagation and extinction ratio in the graphene-based device are numerically investigated. The
proposed terahertz power divider has a 3dB working band about 0.1THz and its extinction ratio reaches about 39.86dB at
the frequency of 7THz. It anticipated that our proposed compact device is potentially interesting for the terahertz wave
integrated circuit technology.
We proposed a simple scheme to manipulate the position of the reflected terahertz wave beam based on the prism/liquid
crystal structure. Both the stationary-phase method and finite element method are used to analyze and simulate the
characteristics of the proposed device. To give comprehensive understanding, the position of the reflected terahertz wave
beam is verified in simulation by using the COMSOL Multiphysics software. Numerical calculation results show that the
proposed terahertz wave switch a high extinction ratio (35dB for TE polarization and 30dB for TM polarization). This
provides an attractive way for creating a simple structure and compact size terahertz wave switch with acceptable
extinction ratio.
We propose a scheme to manipulate the Goos-Hänchen shift of a terahertz wave reflected from the prism/magnetic dielectric. By adjusting the external applied magnetic field, the refractive index of the magnetic dielectric can be changed, so the Goos-Hänchen lateral shift is dynamically tuned. Numerical calculation results further indicate that the proposed configuration has the potential application for the integrated terahertz wave switch with the extinction ratio of 18.5dB at terahertz wave wireless communication frequency of 0.857THz.
Over the past ten years, electromagnetic terahertz (THz) frequencies region from 100 GHz to 10 THz (or wavelengths of
30μm-3mm) have received extensive attention and investigation. Terahertz wave detection enables direct calculations of
both the imaginary and the real parts of the refractive index without using the Kramers-Kronig relations. There are many
potential applications such as radio astronomy, atmospheric studies, remote sensing, and plasma diagnostics. Photonic
crystal (PC) is a low-loss periodic dielectric medium. With special design and construct the PCs can control the
propagation of THz wave in certain directions with specified frequencies. In this letter, we present the numerical design
and analysis of three kinds of compact terahertz wave beam splitter based on photonic crystals structure. The novel
terahertz wave polarizing beam splitter has been designed and calculated through finite element method. The simulation
results show that the proposed polarizing beam splitter has high efficiency and a high extinction ratio. We confirm
theoretically that the photonic crystal structures can be used for separating TE and TM-polarized modes of the
electromagnetic waves in the terahertz range.
There are increasing demands for experiments in terahertz frequencies, in different areas such as biotechnology,
nanotechnology, space science, security, terahertz wave communications, and plasma diagnostics. For potential
applications, the functional devices, such as beam polarizers, modulators and filters, are crucuial components for a
terahertz system. As a dispensable device for ultrafast information processing and interconnection of terahertz wave
communication, terahertz wave filter has attracted considerable attention. In this paper, we design the terahertz wave
filter structure based on three kinds of photonic crystals structures. The finite-difference time-domain (FDTD) has been
employed to analysis the performances of these terahertz wave filters. The simulation results show that these designed
filters exhibit excellent transmission performance such as high transmission at the central frequency, adjustable
bandpass, and good rejection of the sideband frequencies. Three kinds of compact and integrated terahertz wave filters
are obtained.
In the past decade, spectroscopy and imaging in the terahertz region (0.1-10 THz) of the electromagnetic spectrum has
been applied in both basic research and potential industrial applications, such as medical diagnosis, security screening,
radio astronomy, atmospheric studies, short-range indoor communication, chemical, biological sensing, medical and
biological imaging, and detection of explosives. In this paper, we design a narrow bandpass terahertz wave filter using
three kinds of two-dimensional photonic crystals. By using finite-difference time-domain (FDTD) method, we examined
the transmittance spectra for the proposed terahertz wave filter. The simulated results show that the proposed filter
exhibit excellent transmission performance such as high transmission at the central frequency, adjustable bandpass, and
good rejection of the sideband frequencies.
With the realization of terahertz wave generator and detector, electromagnetic terahertz wave wavelength range
(30μm~3000μm) attracted significant attention and has been extensively investigated. Many potential applications of
terahertz waves have been dramatically explored including medical diagnosis, security screening, military detection,
radio astronomy, atmospheric studies, and communication. In this paper, we proposed a kind of photonic crystal fiber
with Panda eyes structure. Using finite element analysis method, the transmission properties of Panda eyes photonic
crystal fiber in terahertz wave regime was analyzed. The results show that terahertz photonic crystal waveguide with a
low transmission loss can be designed if there are suitable parameters. When the transmission frequency f=0.5THz and
d/Λ=0.8, the minimum transmission loss is less than 0.5dB/m.
Terahertz wave is a kind of electromagnetic wave ranging from 0.1~10THz, between microwave and infrared, which
occupies a special place in the electromagnetic spectrum. Terahertz radiation has a strong penetration for many media
materials and nonpolar substance, for example, dielectric material, plastic, paper carton and cloth. In recent years,
researchers around the world have paid great attention on terahertz technology, such as safety inspection, chemical
biology, medical diagnosis and terahertz wave imaging, etc. Transmission properties of two-dimensional metal
microstrip structures in the terahertz regime are presented and tested. Resonant terahertz transmission was demonstrated
in four different arrays of subwavelength microstrip structure patterned on semiconductor. The effects of microstrip
microstrip structure shape were investigated by using terahertz time-domain spectroscopy system. The resonant terahertz
transmission has center frequency of 2.05 THz, transmission of 70%.
Pulsed THz time-domain spectroscopy is a coherent technique, in which both the amplitude and the phase of a THz pulse
are measured. Recently, material characterization using THz spectroscopy has been applied to biochemicals,
pharmaceuticals, polymers and semiconductors and has given us important information. Moreover, THz imaging has
progressed and is expected to be applicable for the identification of narcotics and explosives. The most important and
characteristic point of THz spectroscopy is said to be its ability to observe intermolecular vibrations in contrast to
infrared spectroscopy (IR), which observes intramolecular vibrations. Coherent detection enables direct calculations of
both the imaginary and the real parts of the refractive index without using the Kramers-Kronig relations. Terahertz wave
spectroscopy has been used to study the properties and absorption spectra characteristic of materials. In this paper, the
spectral characteristics of cow skin, pig skin sheep skin, horse skin and deer skin have been measured with terahertz
time-domain spectroscopy in the range of 0.1~2.0THz. The results show that THz-TDS technology provides an
important tool for quality analysis and detection of leathers.
Terahertz radiations, which refer to the frequencies from 100GHz to 10THz, lie in the frequency gap between the
infrared and microwave, have received considerable attention during the past decades. Due to their special prosperties,
THz radiations have been applied in many fields such as gases, semiconductors, explosives materials, and environment
pollutants. The technique is based on recording the time dependence of the electric field of a short electromagnetic pulse
transmitted through a sample. The ratio of the Fourier transforms of the data recorded with and without the sample yields
the complex transmission coefficient of the sample in the frequency domain. The absorption coefficient and the
refractive index of the material studied are directly related to the amplitude and phase respectively of the transmitted
field. Terahertz wave filter, a frequency-selective surface structure, has been characterized by terahertz time-domain
spectroscopy in the region from 0.1 to 3THz. We have compared THz-TDS measurement and calculation results of the
mode-matching theory of the terahertz wave filter, and find that the two data sets agree very closely. The peak of the
transmittance of about 90.5%occurs at 0.45THz for the first case and the peak of the transmittance of about 89.4% occurs
at 0.79THz for the second case.
The terahertz (THz) band, which refers to the spectral region between 0.1 and 10THz, covers the fingerprints of many
chemical and biological materials. Within the past few years, there are increasing demands for experiments in terahertz
frequencies, in different areas such as biotechnology, nanotechnology, space science, security, chemical and biological
sensing, terahertz wave communications, and medical diagnostics. For potential applications, the functional devices,
such as beam polarizers, switchs and filters, are crucial components for a terahertz system. Terahertz wave filter based
on two kinds of microstrip resonant structures, has been characterized by terahertz time-domain spectroscopy in the
region from 0.1 to 3THz. The experimental results for the frequency dependence of the transmittance of the terahertz
wave filter show that the terahertz wave transmittance peak is of 79.5% at 0.5THz and 82.5% at 0.81THz.
By using terahertz time domain spectroscopy (THz-TDS) system, the terahertz dielectric properties of various gallium
arsenides were tested in the frequency range extending from 0.2 to 1.5 THz. The power absorption coefficient and
refractive index of various resistivity gallium arsenides were measured and compared. The refractive index of the high
resistivity and ultra-high resistivity GaAs are equal to be 6.53 and 5.9, respectively. The variation of the refractive index
of the GaAs was less than 1%, ranging from 0.2 to 1.5THz, but the absorption coefficient of the ultra-high resistivity
GaAs showed very different frequency-dependent behaviors, ranging from 0.02cm-1 to 2.21cm-1, within the
investigated frequency range. The results show that the ultra-high resistivity GaAs will be a good candidate material for
terahertz transmission waveguide.
In this letter, the spectral characteristics of cotton in the range of 0.2 ~ 2.5THz have been measured with THz timedomain
spectroscopy. Its absorption and refraction spectra are obtained at room temperature in nitrogen atmosphere. It is
found that cotton has the spectral response to THz waves in this frequency region. The results provided in this paper will
help us to study the THz application to cotton commercial transaction inspection further.
We propose and experimentally demonstrate a novel compact and integrated terahertz waveguide, which consists of
silicon photonic crystals with triangular lattice and a line defect waveguide in photonic crystal (PC) slabs. We also
directly measured the propagation loss of the line defect waveguides and obtained a value of 0.99dB/mm. The observed
waveguiding characteristics agree very well with three-dimensional finite difference time-domain calculations.
In order to observe the spectroscopic characteristics of metallic ion in soil in terahertz region, terahertz time-domain
spectroscopy (THz-TDS) was used to analyze the absorption coefficient and refractive index in the frequency range 0.2
~1.6 THz at room temperature. In the present work, we designed several kinds of soil samples (i.e. different content
copper sulphate and zinc sulphate in soil).The terahertz time-domain spectra of samples were measured. The
experimental results indicate that the metallic ion in soil has many distinct characteristic spectra between 0.2 and
1.6THz. This study can not only assign the characteristic absorption of the sample, but also can provide the absorption
frequencies in wider effective spectra range. The results show that the THz-TDS can be used to measure the metal
residues in the soil.
The absorption spectra of rice bran oil in the frequency range of 0.2~1.6THz has been measured with terahertz timedomain
spectroscopy (THz-TDS) at room temperature in nitrogen atmosphere. It is found that hexadecanoidc acid and
octadecanoic acid contained in rice bran oil has the spectral response to terahertz waves in this frequency region.
Simultaneously, the corresponding theoretical spectra were given by using DFT methods with the aid of Gaussian03. The
experimental spectra are well comparable with the calculated spectra and these results mutually validated both
approaches. It was found that the absorption peaks of the two molecules obtained by theoretical were in good agreement
with the experimental results. The research results prove the feasibility of applying THz-TDS technique to detect and
identify of main component of edible oil. Furthermore, the result s provided in this paper will help us to study the THz
application to food quality evaluation or safety inspection further.
The spectral characteristics of corn oil after five minutes and ten minutes of boiling in the rang from 0.2THz to 1.5THz
have been measured with THz time-domain spectroscopy (THz-TDS) at room temperature in nitrogen atmosphere. A
novel iterative algorithm is employed to determinate the optical properties considering the effect of the cuvette. The
refractive indices of the two corn oil samples show slow a decrease as the terahertz wave frequency increases. The power
absorption coefficients increase as the frequency increases within the investigated terahertz wave frequency range. The
results provided in this paper will help us to study the THz application to seed oil quality and safety detection further.
Over the past ten years, electromagnetic terahertz (THz) frequencies region from 100 GHz to 10 THz (or wavelengths of
30 μm ~3 mm) have received extensive attention and investigation. Terahertz wave detection enables direct calculations
of both the imaginary and the real parts of the refractive index without using the Kramers-Kronig relations. There are
many potential applications such as radio astronomy, atmospheric studies, remote sensing, and plasma diagnostics.
Shoes, neckties and sofa, etc are mainly made of skin of animal, imitated skin and artificial leather. It has important
practical value to component analysis and quality assessment by measuring absorption, refractive index, and other
optical parameters. In this paper, the spectral characteristics of sheepskin, imitated sheepskin and artificial leather have
been measured with terahertz time-domain spectroscopy (THz-TDS) in the range of 0.1~2.0THz. The results show that
there have not absorption peak in the absorption spectrum of the sheepskin. However, it is found that there are three
absorption peaks in the absorption spectrum of the artificial leather at the frequency of 1.13THz, 1.21THz, and 1.36THz,
respectively. The potential application of the leather in THz frequency region is also discussed.
Recently, there has been a remarkable effort in employing terahertz (THz) spectroscopy for investigating material
properties. Pulsed THz time-domain spectroscopy is a coherent technique, in which both the amplitude and the phase of
a THz pulse are measured. Coherent detection enables direct calculations of both the imaginary and the real parts of the
refractive index without using the Kramers-Kronig relations. In this letter, the terahertz absorption spectra and the
refractive indices of olive oil were measured by using terahertz time-domain spectroscopy (THz-TDS) in the frequency
range extending from 0.2 to 2.5 THz. The terahertz dielectric properties of olive oil were characterized by THz-TDS, and
the consistency with the known parameters was identified. A novel iterative algorithm improves the existing data extraction algorithms and further enhances the accuracy of the parameter extraction for terahertz time-domain spectroscopy. The results obtained in this study suggest that the THz-TDS method is a useful tool for vegetable oils characterization in the far infrared region. This method can be applied not only to terahertz time-domain spectroscopy but also to any kind of optical constant measurement in the time domain.
Recently, there has been a remarkable effort in employing terahertz (THz) spectroscopy for investigating material properties. THz-TDS has been employed to investigate a wide variety of materials, including environment pollutants, semiconductors, polymers, explosive materials, and gases, etc. In this letter, the spectral characteristics of cotton in the range of 0.2~2.5THz have been measured with THz time-domain spectroscopy. Its absorption and refraction spectra are obtained at room temperature in nitrogen atmosphere. It is found that cotton has the spectral response to THz waves in this frequency region. The results provided in this paper will help us to study the THz application to cotton commercial
transaction inspection further.
Many materials were previously studied using far-infrared Fourier transform spectroscopy (FTS) in transmission and
reflection modes. Recently, there has been a remarkable effort in employing terahertz time-domain spectroscopy (THz-TDS) for investigating material properties, including environment pollutants, semiconductors, polymers, explosive
materials, and gases, etc. Since the absorption coefficient and the refractive index of the material studied are directly
related to the amplitude and phase respectively of the transmitted field, both parts of the complex permittivity can be
obtained by THz-TDS. In this letter, the optical properties of peanut oils in the frequency range from 0.2 to 2.5 THz were
studied by employing terahertz time-domain spectroscopy. Several peanut oils, such as clean unused peanut oil, peanut
oil after five minutes of boiling, and peanut oil after ten minutes of boiling were tested. The time delays of clean unused
peanut oil, peanut oil after five minutes of boiling, and peanut oil after ten minutes of boiling are 8.33ps, 8.46ps and 8.46ps, respectively. The refractive indices of the three oil samples show slow a decrease as the terahertz wave frequency increases. The power absorption coefficients increase as the frequency increases within the investigated terahertz wave frequency range.
We have measured the absorption spectrum of three kind resistivity p-type silicons by backward-wave oscillator
(BWO).The absorption spectrum is examined and analyzed by least square method. The refractive index, absorption
coefficient, and dielectric functions of various resistivity p-type silicons are obtained in the frequency range extending
from 0.23 THz to 0.375 THz. The experimental results indicate that the absorption coefficient of the p-type silicons are
decreased with the resistivity increase and its least absorption coefficient equals 3.87x10-4 cm-1. Our results demonstrate
that the applicability of the backward-wave oscillator THz absorption spectroscopy to p-type silicon characteristic
analysis by calculating the absorption spectra. This work establishes the basic spectra data for the various resistivity ptype
silicons are very significative to design the terahertz waveguide with low loss.
A novel high-speed optical switch based on organic coumarin waveguide is presented. The device principle is based on
influencing the bend loss in a waveguide by changing the refractive index contrast defining the guide. A low power
femtosecond laser is used to excite the cladding of the curved waveguide. The beam propagation method is employed in
the numerical simulation. The designed optical switch has a large extinction ratio and rapid response time (about 1.2ps).
The terahertz dielectric properties of GaAs were tested in the frequency range extending from 0.23 THz to 0.375 THz by
using backward-wave oscillator (BWO). The terahertz refractive indices, the absorption spectra and the dielectric
functions of various resistivity GaAs were measured and compared. The experimental results indicate that the absorption
coefficient of the GaAs is decreased with the frequency increasing and its least absorption coefficient equals 3.87x10-4
cm-1. Our results demonstrate that the applicability of the backward-wave oscillator THz absorption spectroscopy to
GaAs characteristic analysis by calculating the absorption spectra. This work establishes the basic spectra data for GaAs
is very significative to design the high efficiency terahertz wave antenna.
In this paper, a compact optical modulator using negative refractive material slow-wave waveguide is proposed. The
finite element method (FEM) has been employed to analysis the performances of the novel modulator. The results show
that the size of the novel optical modulator has low power consumption, compact size, easy fabrication, and the cost. Its
dimension is only 40μm-long. The size of the novel optical modulator is 100 times shorter than that of the conventional
lithium niobate optical modulator. It has a potential application for future optical communication systems.
Using negative refractive material slow-wave waveguide, a compact and integrated optical modulator is proposed for the
first time to our knowledge. The slow group velocities of light, which are readily achievable in negative refractive
material waveguide, can dramatically increase the induced phase shifts caused by small changes in the refractive index.
This slow propagation is illustrated with a finite-difference time-domain simulation. Modulation operation was
demonstrated by using a 40 μm-long negative refractive material slow-wave waveguide of a Mach-Zehnder
interferometer (MZI) structure. The modulation depth is 98%.The size of the novel optical modulator is 100 times
shorter than that of conventional MZI optical modulator.
A broadband travelling-wave electro-optical modulator based on teflon substrate is proposed. Finite element method is
employed to analyze the performance of the proposed modulator. The relations between the structure parameters and the
properties of the modulator have been investigated. The optimized structure parameters of the modulator are obtained.
The results show that the modulator has wide modulation bandwidth, low half-wave voltage, and perfect impedance
match.
In this paper, we have proposed a novel compact sub-terahertz wave modulator based on silicon photonic crystals. In our
proposed structure, the photonic crystals are made up of p-i-n silicon. As the free carriers are injected, the photonic band
gap of p-i-n silicon photonic crystals shifts. The light modulation mechanism of the novel sub-terahertz wave modulator
is based on a dynamic shift of the photonic band gap (PBG). The finite-difference time-domain (FDTD) method is used
to investigate the performances of the designed sub-terahertz wave modulator. The simulation results show the sub-terahertz
wave modulator with a high extinction ratio (-40 dB), low insertion loss (-1dB), rapid response time, and small
size can be obtained. Being its small size, the novel sub-terahertz wave modulator can be used in future sub-terahertz
wave integrated circuits.
In this letter, a new type of optically controllable, terahertz wave switch using high resistivity silicon wafer is developed.
A high resistivity silicon is a lossless dielectric material at terahertz wave without optical excitation. When a silicon
wafer is optically excited, free carriers are generated, and the silicon wafer becomes a lossy dielectric. We study
theoretically and demonstrate experimentally light controllable terahertz wave of the high resistivity silicon wafers. The
results show that a more than 15dB attenuation of the novel device is obtained at frequency of 0.3THz. The proposed
structure is useful for developing low cost switch in the terahertz wave region.
In this paper, a novel compact optical modulator based on silicon photonic crystals /nano-montmorillonite is proposed.
The two-dimensional silicon photonic crystal with triangular lattice and a line defect waveguide formed by a missing
row of air holes in the Γ -K direction. The lattice constant is a, and the diameter of the holes is d=0.4a. The holes are
filled with the nano-montmorillonite electrorheological fluid, which is made of nanometer sized nano-montmorillonite.
The light modulation mechanism of the novel modulator is based on a dynamic shift of the photonic band gap. We have
investigated its light modulation performance by using the finite-difference time-domain method. The numerical results
show that an excellent optical modulator at a wavelength of 1550nm is achieved. The novel modulator has a high
extinction ratio (close to -40dB) and small size (around 10μm). It is very suitable for forthcoming photonic integrated
circuits.
In this letter, we have proposed a novel compact terahertz wave switch based on photonic crystals. The OFF-ON
mechanism of the novel terahertz wave switch is based on a dynamic shift of the photonic band gap. The two-dimensional
finite-difference time-domain (FDTD) method is used to investigate switch properties of the terahertz wave
switch. The simulation results show that the terahertz wave switch size is about 6.8mm. The novel terahertz wave switch
can be used in future terahertz-wave communication and detection systems.
A novel electro-optical modulator using GeO2 doped silica waveguides based on silicon substrate is proposed. The
modulator is analyzed and designed with the finite element method. The simulation results show that the designed
modulator operates with a 3dB optical bandwidth of 56.6GHz, a half-wave voltage of 8.9V and a characteristic
impedance of 51.8Ω at 1310nm wavelength. The presented modulator can be fabricated easily using Si-based very large-scale
integrated technology and is very suitable for optoelectronic integrated circuits.
A new method for bend loss in a curved polymer/SiON waveguide is presented and it is used to design a novel variable
optical attenuator. The device principle is based on influencing the bend loss in a waveguide by changing the lateral
refractive index contrast defining the guide. The beam propagation method is employed in the numerical simulation. The
designed optical attenuator has a maximum attenuation of -46.1 dB. The response time was below 5 ms.
Rayleigh scattering loss of photonic crystal fiber is numerically analyzed by using a full-vector finite element method.
The constant tangential/linear normal vector basis functions are employed to investigate the Rayleigh scattering loss
effect of the photonic crystal fiber structure. Numerical results show that Rayleigh scattering loss is great dependence on
the fiber structure parameters. Rayleigh scattering loss of PCF can be effectively reduced by improving the fiber
fabrication techniques.
A novel optical switch based on silicon/kaolinite photonic-crystal line-defect waveguides is proposed. The optical switch
is analyzed and simulated with the finite-difference time-domain (FDTD) method. The designed optic switch operates
with high extinction ratio of 40 dB, and compact size of 10 μm at 1550 nm wavelength. Being a compact in size and
silicon base photonic crystal, the device is very suitable for high-density integrated optics circuits.
We proposed a novel compact and integrated optical modulator, which consists of p-i-n silicon photonic crystals with
triangular lattice and a line defect waveguide. The device operation is based on a dynamic shift of the photonic band gap
(PBG), which is induced change in the silicon refractive index by the free carrier injection. We have numerically
analyzed and investigated its light modulation performance by using the finite-difference time-domain method. Being a
small size and high performance, the designed optical modulator can be used in photonic integrated circuits.
A novel fiber type traveling-wave modulator is developed. The finite element method (FEM) has been used to analyze
the performance of the proposed modulator with coplanar waveguide (CPW) electrode structures. The optimized
structures of the traveling-wave modulator are obtained. The results show that the novel modulator has a 3dB optical
bandwidth of 112GHz, a half driving voltage of 2.7V, and characteristic impedance of 51.2Ω at 1.55μm wavelength.
We propose a novel Z-cut lithium niobate electro-optic modulator based on a Si2N2O substrate. The structure is analyzed using the finite element method. The novel modulator with 3-dB optical bandwidth, half-wave voltage, and characteristic impedance at 1.5-µm wavelength are 120 GHz, 3.5 V and 50.2, respectively. The simulation results show that the modulator can achieve wide bandwidth, low half-wave voltage, and a good impedance match. The modulator has good potential for high-speed optical transmission systems.
In this letter, we propose a novel optical modulator based on GaAs photonic crystals and investigate its optically properties numerically by using the finite-difference time-domain method. The position of the cutoff frequency can be varied by free carriers injection, and the band gap shift can be observed. Band gap shift is used to modulate light. Bing several micrometers length, low insertion loss, and large extinction ratios, the modulator can be used in ultra-small and ultra-dense photonic integrated circuits.
In this paper, we have proposed a novel compact electro-optical switch based on silicon/montmorillonite (MMT) photonic crystals and investigate its optically controlled on-off switch properties numerically by using the finite-difference time-domain method. The numerical simulation results show an excellent electro-optic switch at a wavelength of 1300nm was achieved with applied voltage as low as 0.5V, an extinction ratio of 20dB and a length of only 15μm.
In this letter, a novel broadband optical fiber type M-Z modulator with traveling-wave electrode is proposed. Since the waveguides are formed using special optical fiber, the microwave field is concentrated in the optical fiber regions. The finite element method has been used to analyze the microwave equivalent refractive index and characteristic impedance. Then, the performance of the modulator has been simulated using the neural network. The calculated and simulation results are shown in figures. Compared with the conventional modulator, the novel modulator can easily obtain the velocity matching and impedance matching. Using this structure, we have developed a fiber type M-Z modulator with 80GHz 3dB bandwidth, 1.18V half-wave driving voltage, and 55.5Ω impedance.
Elaborate theoretical analysis has been done for the modulation characteristics of semiconductor 1aser and analytical expression has been deduced through the research of rate equation of semiconductor 1aser. A neural network model analyzing of the modulation characteristics of semiconductor laser is developed. Using the model, we find that the simulation result is well agreed with theoretical analysis result. Furthermore, a semiconductor 1aser is design by the model. The research shows that the method has significant direction for the design of semiconductor 1aser.
In this paper, a LiNbO3 optical-fiber modulator with CPW electrode is discussed. Being use the LiNbO3 optical fiber as the transmission channel of light in this structure, the modulator has less LiNbO3 than the conventional LiNbO3 waveguide modulator. It effectively decreases the effective dielectric coefficient of microwave and realizes velocity matching and low half-wave driving voltage. The characteristic impedance, refractive index and bandwidth of the modulator have been derived using finite element method. The optimal structure of modulator is presented.
A measuring principle and method about rotatory element ε' in the tensor dielectric coefficient of a rotatory optical fiber is put forward in this paper. First the rotatory angle ψ and rotatory coefficient V is measured which make us understand the rotatory characteristic of the optic fiber. On the basis of that the ε'; is measured by the one of measurement of ψ, I or Hb. The measuring of ε' is very important for analysis and calculation the rotatory fiber by electromagnetic theory.
The basic theory of rotatory optical fiber was discussed. The electromagnetic field components, basic parameters of the fiber were evaluated as the functions of the argument ε' which is the rotatory element in the tensor dielectric coefficient matrix ε of the fiber .The calculating results were shown by the curves. In addition, a new expression about the relation between ε' and applied magnetic field Hb was demonstrated, by that the tensor dielectric coefficient of the rotatory optical fiber can be easily evaluated.
In this paper, a novel electro-optic modulator-optical fiber type traveling wave modulator was proposed and analyzed. Its modulation bandwidth, half-wave driving voltage and characteristic impedance have been analyzed and calculated. Furthermore, considering these factors, we could get an optimized modulator. The result shows that the novel fiber type traveling wave modulator has the advantages of wide bandwidth, low driving voltage and impedance match. It meets the need of high speed and broadband optical communication.
The coupling length and coupling ratio is defined as input and output respectively, which are used to train the neural network model. Radial base function neural network model is built for optical fiber direction coupler, which is in turn simulated and designed through the model. This method has the advantages of speediness, accuracy and reliability, which are identified by the design example. It can be used to design the other kind of optical passive device. This way is a novel design approach, which can save the cost of device design, decrease period of design and has a good prospect of application.
Back Propagation (BP) and Radial Base Function (RBF) neural network methods have been used to design optical fiber temperature sensor probe which is used in medical treatment. Data trained for neural network are gained from experiment and interpolation. New kind of fiber optic temperature sensor with the best sensitivity was designed and made by the method. The selected design scheme is proved to be feasible in the experiment. This method has the characteristics of accuracy, credibility and knowledge-aid design, which are identified by the experiment. This way can save the device cost of design and decrease period of design, which has a good prospect of investigation and application.
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