A multichannel all fiber current sensor that can be used to measure currents at different positions simultaneously is presented in the paper. Each sensor head uses single-polarization single-mode devices and loop scheme to realize current measurement. All the sensor heads are connected via a series structure and the measured results are received by only one photo-detector based on the principle of time-division multiplexing. Theory and experiment prove that the sensor is feasible.
In this paper, we demonstrate a novel all-fiber current sensor using ordinary silica fiber and the fiber loop architecture that can be used to improve current sensitivity. In order to improve the efficiency of the sensor and reduce cost, we present a multichannel all-fiber current sensor based on the principle of time-division multiplexing. To illustrate the principle, we show the typical dual-channel all-fiber current sensor in our experiment. It shows that the currents at two different points can be measured simultaneously. In addition, we find by measurement that the dual-channel fiber current sensor has good linear responses dependence of the variation of the degree of polarization ∆P on the current intensity I for two channels respectively. Every channel is affected by the current alone, requires a separate calibration.
In this paper, the 1×5 optical splitters (OSs) based on 2D rod-type silicon photonic crystal embed cascaded
self-collimation (SC) ring resonators (CSCRR) was proposed. The 1×5 OSs consist of eight beam splitters, which are
formed by varying the radii of the rod. With self-collimation effect, we can manipulate the light’s propagation in the OSs.
Here we consider TM modes. Utilizing multiple-beam interference theory, the theoretical transmission spectra at
different outputs were analysed. These transmission spectra can help us to set the radii of eight slitters properly, for we
can control the light coming out from five ports with the light-intensity ratio we need. Meanwhile these outputs’
transmission spectra were investigated by the finite-difference time-domain (FDTD) method. The simulative results have
an agreement with the theoretical prediction. The 1×5 OSs will have practical applications in photonic integrated circuits.
We propose a compact Terahertz (THz) wave broadband reflector based on the effect of guided mode resonance in photonic crystal slabs. The photonic crystal slabs consist of a square array of circular air holes in silicon. A novel method based on a map of localized bandwidth with defined reflectivity is introduced to analyze the impact of normalized thickness and hole size. The rigorous coupled-wave analysis (RCWA) technique is then applied to analyze its performance. The numerical simulations show that the proposed configuration can offer a broadband frequency range from 2.27THz to 2.89THz with beyond 95% reflectivity.
We devised a new configuration of optical logic gates based on a single hexagonal-lattice photonic crystal ring resonator (PCRR) composed of two-dimensional (2D) cylindrical silicon rods in air. The modal behavior of the proposed logic gates was comprehensively analyzed with a topology optimization technique based on the principle of beam interference and perturbation theory. It was then numerically verified by using a 2D finite-difference time-domain technique. The predictions have a very good agreement with the numerical results. This new single PCRR can really function as NOT and NOR gates. And the logic "0" and "1" of the hexagonal ring can be defined as less than 8% and greater than 86%, respectively, much better than earlier reported square-lattice results.
A tunable drop filter (TDF) based on two-dimensional photonic crystal (PC) self-collimation ring resonator (SCRR) is
proposed. The PC consisting of square-lattice air cylinders in silicon has square-shaped equal frequency contours (EFCs)
in the wavevector space at the frequencies between 0.172-0.188<i>c/a</i> for TE modes. The SCRR includes two mirrors and
two splitters. The air holes inside the SCRR are infiltrated with a kind of liquid crystal whose ordinary and
extraordinary refractive indices are 1.522 and 1.706, respectively. The effective refractive index <i>n</i><sub>eff</sub> of liquid crystal
depends on the applied electric field. Simulated with the FDTD method, the transmission spectra at the drop port of
SCRR are in the shape of sinusoidal curves with uniform peak spacing between 0.172-0.188<i>c/a</i>. Transmission peaks
will shift to the lower frequencies when <i>n</i><sub>eff</sub> is increased. When <i>n</i><sub>eff</sub> changes from 1.522 to 1.706, the peaks will
experience red-shift over 0.003<i>c/a</i>. So this SCRR can work as a tunable drop filter. For the operating wavelength
around 1550nm, its dimensions are only tens of microns.
We proposed a new channel drop filter (CDF) based on race-track photonic crystal ring resonator (PCRR) composed of
square-lattice cylindrical silicon rods in air. Two representative scenarios, parallel and perpendicular, related to the
direction of race track and bus channel waveguide, are comparably studied by using 2D finite-difference time-domain
technique. A good set of parameters with adequate modal spacing can be determined by adjusting the amount and size
of scatterers. By optimizing the relationship among surrounding periods, race-track ring size and coupling strength,
more than 150 spectral quality factor and 93.9% dropped efficiency can be achieved at 1370-nm channel for one single
race-track PCRR. These findings enhance and enrich the PCRRs as an alternative to current micro-ring resonators for
ultra-compact WDM components and high density photonic integration.
We report a new configuration of logic gates based on single hexagonal-lattice PCRR composed of cylindrical silicon
rods in air. Two types of inner ring including regular hexagonal and circular are numerically discussed by using 2D
finite-difference time-domain (FDTD) technique. The impact of surrounding periods and scatterers like size and relative
phase at each input port was investigated. The logic '0' and '1' of hexagonal ring can be defined as less than 17% and
greater than 85%, respectively, much better than early reported square-lattice results. The simulation results also proved
that photonic logic gates based on this new single PCRR can really function as NOT and NOR gates, respectively.
These findings make PCRRs potential applications for all-optical logic circuits and ultra-compact high density photonic
A new optical channel drop filter configuration was proposed based on two-dimensional (2D) square-lattice 45° photonic
crystal ring resonators (PCRRs). The ring was formed by removing the line defect along ΓM direction instead of
conventional ΓX direction. Its spectral information including transmission intensity, dropped efficiency and quality
factor affected by different configurations like single-ring PCRR and cascaded dual-ring PCRR was numerically
analyzed with 2D finite-difference time-domain technique. More than 830 spectral quality factor and 90% dropped
efficiency can be achieved at 1550-nm channel for one single-ring PCRR. Two different light wavelengths can be
dropped simultaneously for cascaded serial dual-ring PCRR. These findings make the 45° PCRR optical channel drop
filters as an alternative to current micro-ring resonators for ultra-compact WDM components and high density photonic
The self-collimation frequencies (SCFs) in two-dimensional photonic crystals (2-D PhC) have been investigated
systematically by the plane-wave expansion method. In the wave-vector space, the square-lattice 2-D PhCs have some
square-shaped equifrequency contours (EFCs) both for TE modes and for TM modes. Narrow-beam lights with these
frequencies can propagate in the directions normal to the flat borders of the EFCs without any significant broadening,
which is known as self-collimation effect. We consider the 2-D PhCs consisting of a square lattice of air cylinders in a
dielectric material and the 2-D PhCs consisting of a square lattice of dielectric cylinders in air respectively. Calculation
results show how SCFs of TM and TE modes change with the radius of cylinders and the refractive index of the material.
These results can be applied to designing the PhC devices based on self-collimation effect.
A theoretical model of wavelength interleaver, which is based on an asymmetric Mach-Zehnder interferometer (AMZI) constructed in a two-dimensional photonic crystal (2D PhC), is proposed and numerically demonstrated. The 2D PhC consists of a square lattice of dielectric cylindrical rods in air. The AMZI includes two mirrors and two splitters. Light propagates between them employing self-collimation effect. The two interferometer branches have different path lengths. By using the finite-difference time-domain method, the calculation results show that the transmission spectra at two AMZI output ports are in the shape of sinusoidal curves and have a uniform peak spacing in the frequency range from 0.191<i>c/a</i> to 0.200<i>c/a</i>. When the path length of the longer branch is increased and the shorter one is fixed, the peaks shift to the lower frequencies and the peak spacing decreases nonlinearly. Consequently, the transmission can be designed to meet various application demands by changing the length difference between the two branches. For the dimensions of the wavelength interleaver are about tens of central wavelengths, it may be applied in future photonic integrated circuits.
A Fabry-Perot (FP) etalon constructed in a two-dimensional photonic crystal (2D PhC) utilizing self-collimation effect is
proposed and investigated. The 2D PhC consists of a square lattice of air holes in silicon. It has square-shaped equal
frequency contours (EFCs) in the frequency range of 0.275-0.295c/a for TE modes. The FP proposed consists of two
PhC reflectors and one cavity between them. Light propagates in the photonic crystal employing self-collimation effect.
The two reflectors have reflectivities of around 97.5% in the frequency range 0.275-0.295c/a. The FDTD calculation
results show that the transmission spectrum of the FP etalon has a uniform peak spacing between 0.275c/a and 0.295c/a.
The transmission spectrum shifts to the lower frequency as the refractive index of a fluid filling in the air holes in the FP
cavity is increased. Therefore this etalon can work as an optical sensor for a gas and a liquid. The fluids whose refractive
index vary within 1.0-1.5 can be sensed and detected. Its dimensions are only about tens of microns when the central
operating wavelength is equal to 1550nm. So it can be applied as a micro-scale sensor.
In this letter, we present an improved coupled-mode theory applied to the optical-fiber directional coupler with a large overlap between the evanescent electromagnetic fields of two fibers. The analysis is based on a method of the quantum mechanics for the hydrogen molecule ion, where a new couple of local orthogonal modes corresponding to the fiber 1 and 2 are introduced. We may obtain the coupled-mode equations of local modes and the simple formulas of the output powers from coupler, in which, the overlap integral between the evanescent fields of two fibers is taken account of as an second order approximation. A new conclusion from this theory is that a coupling ratio with 100% can't be reached for a lossless coupler with a sufficiently small distance between two fibers.