We demonstrate a novel fiber-optic hydrophone that use a fiber Bragg grating (FBG) as
a sensing element. The operation principle is based on the modulation of birefringence of the FBG
by high-frequency ultrasound. By measuring the amplitude of the first Stokes parameters of the
transmitted light in FBG using a in line polarimeter, the amplitude and frequency of acoustic
pressure can be determined. The FBG hydrophone has a linear response to acoustic pressure, and
the sensitivity and dynamic range of the sensor are studied.
A novel dispersion compensating fiber with multiple windows is firstly proposed. The proposed DCF is based on hybrid
photonic crystal fiber. This type of DCF gets a multiple negative dispersion windows by the coupling between the hybrid
guiding mode in the edge of each band-gap and the index guiding mode in the cladding deficit area. This is very different
from the ordinary dual-core mechanism. This proposed DCF can be widely used in dispersion compensating system, the
photonic generation of UWB signals, the pulse forming system and the compressing of optical soliton.
In this paper the transmission and polarization properties of fiber Bragg gratings with magnetically induced circular
birefringence are discussed. The evolutions with wavelength of transmission spectrum and the polarization-dependent
parameters for different circular birefringence, grating lengths and input polarizations are analyzed. We demonstrate that
the third Stokes parameter and ellipticity evolutions contain the information about the amount of circular birefringence
and could thus be used to sensor magnetic field value. Three polarizers are used to detect the absolute values of
polarization parameters and hence sense the polarization evolutions.
Fiber Bragg gratings have has been widely used in sensors. We analyze the transmission and polarization properties of magneto-optical fiber Bragg gratings based on coordinate conversion. The simulations demonstrate the influence of magnetic field intensity on the transmission spectrum, the polarization properties by the coupled mode theory, and the Jones formalism. The results show that while a small magnetic field can hardly be detected in the grating amplitude response, it leads to significant polarization properties such as the third normalized Stokes parameter, polarization dependent loss, and ellipticity. We demonstrate that these polarization properties contain information about the magnetic field and can thus be used for magnetic field sensing purposes. The sensitivity and dynamic range depend on the physical parameters of the grating.
Polarization properties of gratings can be used to develop new types of fiber Bragg grating (FBG)-based sensors. In this
paper, the evolutions of states of polarization (SOPs) of transmitted light in linear birefringence gratings are studied by
implementing the Jones formalism and the coupled mode theory. The relationship between the first normalized stokes
parameter and polarization dependent loss is discussed. The results show that the corresponding wavelengthes of PDL
maximum amplitude are the same as that of the first normalized stokes parameter all the while. And both of these two
parameters increase monotonously with birefringence thus can be used for sensor. The effects of transmitted length,
linear birefringence value and incident SOPs on PDL, the first normalized stokes parameter and the polarization states
are discussed. The results show that the SOPs of different wavelengths will spread gradually with the increasing grating
lengths or birefringence values.
In this paper the characteristics of grating structure in magnetic field measurements based on differential group delay of
fiber gratings are analyzed. Theoretical simulations are realized using the coupled-mode theory and transfer matrix
method. The effects of grating parameters of uniform Bragg grating on measurement range and sensitivity are analyzed.
The impacts of chirped, phase-shifted and apodized gratings on DGD peak values are also monitored. FBG transmitted
spectrums and DGD spectrums are recorded by means of an optical vector analyzer (OVA). Both the simulations and
experiments demonstrate that the phase-shifted gratings can obviously improve the sensitivity.
A New magnetic field measurement based on polarization effect of fiber grating was analyzed in theory and
experiment. The simulations show the linear relationship between the peak value of PDL and magnetic field in
certain range. Moreover, this method is temperature insensitive. The precision of this method is 2Gs using the
optical vector analyzer in experiment and agree well with the theory.
Fiber grating is sensitive to the stress, temperature and other entironmental factors. It has caused much attention and has
been used widely. In this paper a new magnetic field measurement using different group delay (DGD) of fiber grating is
proposed. When the magnetic field applied the refractive index difference of the two circularly polarized light in fiber
grating will be changed because of the faraday effect. So the DGD of fiber grating is changed. Through the formula
derivation in certain condition, the linear relationship between the peak value of DGD and magnetic field in
measurement range is found. Through the simulations the effect of applied magnetic field, fiber length and index
modulation coefficient on the peak value of DGD is shown. On the other hand, the linearity will tend to saturation when
magnetic field exceed the measurement range. So we can determine the mesurement range given design parameters. In
the experiments the DGD of FBG without and with magnetic field are performed. The peak value of DGD increases with
the applied magnetic field linearly. The fit curve of experimental and simulated results is parallel approximately and the
gap is because of the intrinsic DGD of fiber grating. Using the optical vector analyzer with precision of 10-5ps we get the
sensitivity of 0.001Gs in experiment. The simulations and experiments validate this method.
This paper proposes a method of wavelet analysis for de-noising at receiver system in WDM laser inter-satellites communication. Background noises such as galactic noise, sunlight and etc make the received power reduce. The noisy signal is decomposed using wavelets and wavelet packets; then is transformed into wavelet coefficients and the lower order coefficients are removed by applying a soft threshold. De-noised signal is obtained by reconstructing with the remaining coefficients. In this paper, we evaluate different wavelet analysis for de-noising at receiver system in inter-satellites laser communication. Simulation results indicate that if the wavelet de-noising method is used with different wavelet analyzing functions, it will improves the signal to noise ratio (SNR) about 2 dB when the signal frequency is 1.5 GHz.
Next-generation wavelength routing optical networks requiring optical cross connects (OXC) in the network have the ability to direct optical signals from any input interface to suitable output interfaces by configuring their internal embedded optical switch matrices. Optical switches based on MEMS technology have the fundamental advantage of being able to exploit the benefits of free-space interconnection (including low loss and crosstalk, and low polarization- and wavelength-dependence), together with the advantages of integrated optics (including compactness, optical
pre-alignment, and low cost ). Therefore, it offers the possibility of achieving high port-count in a small, low-cost system
with excellent optical quality. In this paper, at first the basic concepts of the two kinds of optical MEMS switches--2-D and 3-D switches are reviewed and the principle of the MEMS switches is introduced. The key parameter in the assembly/packaging of optical components is the insertion losses due to misalignment between the optical components. The misalignment losses are calculated as the coupling coefficient between two Gaussian beams having certain lateral and longitudinal separations and a tilt angle. It's concluded that optical design of a free-space MEMS component is a compromise between lateral misalignment and angular misalignment from the simulations. At last the application of optical MEMS switches in the optical cross-connects is discussed including the configurable WADM
(wavelength-add-drop multiplexer) which can be achieved using 2-D MEMS crossbar matrix switches and the three-dimensional (3-D) microoptical switching system (3D-MOSS).
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