146 research outputs found
Advanced optical modulation and fast reconfigurable en/decoding techniques for OCDMA application
With the explosive growth of bandwidth requirement in optical fiber communication
networks, optical code division multiple access (OCDMA) has witnessed tremendous
achievements as one of the promising technologies for optical access networks over the
past decades. In an OCDMA system, optical code processing is one of the key
techniques. Rapid optical code reconfiguration can improve flexibility and security of
the OCDMA system. This thesis focuses on advanced optical modulations and
en/decoding techniques for applications in fast reconfigurable OCDMA systems and
secure optical communications.
A novel time domain spectral phase encoding (SPE) scheme which can rapidly
reconfigure the optical code and is compatible with conventional spectral domain phase
en/decoding by using a pair of dispersive devices and a high speed phase modulator is
proposed. Based on this scheme, a novel advanced modulation technique that can
simultaneously generate both the optical code and the differential-phase-shift-keying
(DPSK) data using a single phase modulator is experimentally demonstrated. A
symmetric time domain spectral phase encoding and decoding (SPE/SPD) scheme using
a similar setup for both the transmitter and receiver is further proposed, based on which
a bit-by-bit optical code scrambling and DPSK data modulation technique for secure
optical communications has been successfully demonstrated. By combining optical
encoding and optical steganography, a novel approach for secure transmission of time
domain spectral phase encoded on-off-keying (OOK)/DPSK-OCDMA signal over
public wavelength-division multiplexing (WDM) network has also been proposed and
demonstrated.
To enable high speed operation of the time domain SPE/SPD scheme and enhance the
system security, a rapid programmable, code-length variable bit-by-bit optical code
shifting technique is proposed. Based on this technique, security improvements for
OOK/DPSK OCDMA systems at data rates of 10Gb/s and 40Gb/s using reconfigurable
optical codes of up to 1024-chip have been achieved.
Finally, a novel tunable two-dimensional coherent optical en/decoder which can
simultaneously perform wavelength hopping and spectral phase encoding based on
coupled micro-ring resonator is proposed and theoretically investigated. The techniques
included in this thesis could be potentially used for future fast reconfigurable and secure
optical code based communication systems
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Studying the Value of Information Sharing in E-Business Supply Chain Management
The supply chain management of goods and services involves multiple trading partners such as raw-material suppliers, manufacturers, distributors, and retailers. Every one of these trading partners need to determine their requirements, in terms of merchandise, and match them against availability, pricing, and cost of transportation. At every step of the supply chain economics information retrieval is a crucial and recurring process. In this paper we study information sharing as a strategy for improved decision making that can increase the profitability of the entire supply chain. We describe various different models for information sharing and illustrate the benefits of information sharing using ordering relationships among the trading partners of a simple four-node supply chain. In order to examine the relationship between different variables and the well-known bull-whip ejfect, we develop a simulation system to quantify the variables and generate different results in different scenarios. These results are analyzed in this paper, and implications are presented
Boundary stabilization of quasilinear hyperbolic systems of balance laws: Exponential decay for small source terms
We investigate the long-time behavior of solutions of quasilinear hyperbolic
systems with transparent boundary conditions when small source terms are
incorporated in the system. Even if the finite-time stability of the system is
not preserved, it is shown here that an exponential convergence towards the
steady state still holds with a decay rate which is proportional to the
logarithm of the amplitude of the source term. The result is stated for a
system with dynamical boundary conditions in order to deal with initial data
that are free of any compatibility condition
Superresolution of Hyperspectral Image Using Advanced Nonlocal Means Filter and Iterative Back Projection
We introduce an efficient superresolution algorithm based on advanced nonlocal means (NLM) filter and iterative back projection for hyperspectral image. The nonlocal means method achieves the to-be-interpolated pixel by the weighted average of all pixels within an image, and the unrelated neighborhoods are automatically eliminated by the trivial weights. However, spatial location distance is also an important issue to reconstruct the missing pixel. Therefore, we proposed an advanced NLM (ANLM) filter considering both neighborhood similarity and patch distance. In the conventional NLM method, the search region was the whole image, while the proposed ANLM utilizes the limited search to reduce the complexity. The iterative back projection (IBP) is a very famous method to deal with the image restoration. In the superresolution issue, IBP is able to recover the high-resolution image iteratively from the given low-resolution image which is blurred due to the noise by minimizing the reconstruction error, while, because the reconstruction error of IBP is back projection and isotropic, the conventional IBP suffers from jaggy and ringing artifacts. Introducing the ANLM method to improve the visual quality is necessary
Simulation of CSSTs astrometric capability
The China Space Station Telescope (CSST) will enter a low Earth orbit around
2024 and operate for 10 years, with seven of those years devoted to surveying
the area of the median-to-high Galactic latitude and median-to-high Ecliptic
latitude of the sky. To maximize the scientific output of CSST, it is important
to optimize the survey schedule. We aim to evaluate the astrometric capability
of CSST for a given survey schedule and to provide independent suggestions for
the optimization of the survey strategy. For this purpose, we first construct
the astrometric model and then conduct simulated observations based on the
given survey schedule. The astrometric solution is obtained by analyzing the
simulated observation data. And then we evaluate the astrometric capability of
CSST by analyzing the properties of the astrometric solution. We find that the
accuracy of parallax and proper motion of CSST is better than 1 mas( yr1) for
the sources of 18-22 mag in g band, and about 1-10 mas( yr1) for the sources of
22-26 mag in g band, respectively. The results from real survey could be worse
since the assumptions are optimistic and simple. We find that optimizing the
survey schedule can improve the astrometric accuracy of CSST. In the future, we
will improve the astrometric capability of CSST by continuously iterating and
optimizing the survey schedule.Comment: 17 pages, 10 figure
Propagation Characteristics of Oblique Incident Terahertz Wave in Nonuniform Dusty Plasma
Propagation characteristics of oblique incident terahertz wave from the nonuniform dusty plasma are studied using the propagation matrix method. Assuming that the electron density distribution of dusty plasma is parabolic model, variations of power reflection, transmission, and absorption coefficients with frequencies of the incident wave are calculated as the wave illuminates the nonuniform dusty plasma from different angles. The effects of incident angles, number density, and radius of the dust particles on propagation characteristics are discussed in detail. Numerical results show that the number density and radius of the dust particles have very little influences on reflection and transmission coefficients and have obvious effects on absorption coefficients. The terahertz wave has good penetrability in dusty plasma
Reflection and transmission of Laguerre-Gaussian beams in a dielectric slab
Abstract This paper considers the reflection and transmission characteristics of a Laguerre-Gaussian (LG) beam in a dielectric slab. The fields of the reflected and transmitted beams are described based on plane-wave angular spectrum representation. Using the generalized Fresnel amplitude reflectance and transmittance, the reflected and transmitted fields in each region are expressed. With the Taylor series approximation of reflectance and transmittance, the analytical expressions of the total reflected and transmitted fields in the input and output regions are derived. The effects of the beam-waist radius and topological charge on the reflected and transmitted field intensities are simulated and discussed in detail. The centroid shifts of the reflected beam are also presented. It is concluded that the distortion of the intensity distribution including the size of the intensity contour, is influenced by the beam-waist radius and the topological charge of the incident beam. The total intensity of the slab, in particular for the case of the transmitted field, is found to be distinguishable from the case of the single interface
Propagation Characteristics of Oblique Incident Terahertz Wave in Nonuniform Dusty Plasma
Propagation characteristics of oblique incident terahertz wave from the nonuniform dusty plasma are studied using the propagation matrix method. Assuming that the electron density distribution of dusty plasma is parabolic model, variations of power reflection, transmission, and absorption coefficients with frequencies of the incident wave are calculated as the wave illuminates the nonuniform dusty plasma from different angles. The effects of incident angles, number density, and radius of the dust particles on propagation characteristics are discussed in detail. Numerical results show that the number density and radius of the dust particles have very little influences on reflection and transmission coefficients and have obvious effects on absorption coefficients. The terahertz wave has good penetrability in dusty plasma
Reflection,Transmission, and Absorption of Vortex Beams Propagation in an Inhomogeneous Magnetized Plasma Slab
Based on the angular spectrum expansion and the 4x4 transfer matrix method, an investigation into the reflection, transmission, and absorption of vortex beams in an inhomogeneous magnetized plasma slab is presented. The reflected and transmitted electric fields are expressed by the inverse Fourier transform of the product of the reflected and transmitted coefficients and the angular spectrum amplitude of the incident beam. The intensity profiles, as well as the distortion of OAM states in both the reflected and transmitted beams are simulated and discussed. Through this investigation it could be concluded that both the incident angle and the plasma parameters have significant impact on the magnitudes of reflected and transmitted intensities, and the distortion of OAM states. The effects of the magnetic field and the incident angle on the reflectance, transmittance, and absorptance of the power have also been reported
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