At present, the civil aviation airports use the surface surveillance radar monitoring and positioning systems to
monitor the aircrafts, vehicles and the other moving objects. Surface surveillance radars can cover most of the
airport scenes, but because of the terminals, covered bridges and other buildings geometry, surface
surveillance radar systems inevitably have some small segment blind spots. This paper presents a monocular
vision imaging technology model for airport surface surveillance, achieving the perception of scenes of moving
objects such as aircrafts, vehicles and personnel location. This new model provides an important complement
for airport surface surveillance, which is different from the traditional surface surveillance radar techniques.
Such technique not only provides clear objects activities screen for the ATC, but also provides image
recognition and positioning of moving targets in this area. Thereby it can improve the work efficiency of the
airport operations and avoid the conflict between the aircrafts and vehicles. This paper first introduces the
monocular visual imaging technology model applied in the airport surface surveillance and then the monocular
vision measurement accuracy analysis of the model. The monocular visual imaging technology model is
simple, low cost, and highly efficient. It is an advanced monitoring technique which can make up blind spot
area of the surface surveillance radar monitoring and positioning systems.
Raman spectra and infrared imaging systems are used for the study of internal temperatures of PLEDs. The aim is to
investigate the thermal degradation of PLEDs with different current densities. Raman intensity is proportional to the
number of molecules in the next higher vibration energy level, and accurate internal temperature of PLEDs at thermal
equilibrium can be calculated with the ratio of anti-stokes to stokes Raman density by Boltzmann equation. With the
current density of PLED going from 0 mA/cm2 to 169 mA/cm2,it is found that the internal temperature of PLED increases accordingly. When the temperature comes to the glass transition temperature (Tg) of the emission layer, there is a phase change in it and the layer becomes free state as liquid, which is not stable. Local disfigurement in the emission layer results in short circuit between the cathode and the anode of a PLED, and the luminescence of PLED fails. Therefore, Raman spectrum is considered as a good method for detecting temperatures of thin-film semiconductor devices.
A fast and accurate polarization control and stabilization system, which is based on coordinate system transformation, is
experimentally demonstrated. The typical control speed is 50-ms and the output SOP precision is 0.5°.
We present a compact short pulses source, in which the pulses generated by large-signal directly modulated laser diode
are phase-modulated, and it can compress the pulse from 30ps to 5.3ps with 184fs timing jitter.
PMD vectors can be described by Stokes vectors pointing to the direction of slow PSP with a length equal to DGD. Measuring DOP is a way of obtaining DGD information and the direction of PSP can be characterized by scrambling at the transmitter. When totally polarized optical signals (DOP=1) transmit a distance, DOP decreases due to the influence of PMD. However, if the input SOP is aligned to the direction of the PSP, DOP of optical signals remains unchanged. Placing a scrambler at the transmitter, SOP of input signals covers Poincare sphere at a certain frequency. The effect of PMD on SOPs in different directions changes with transmission, and the output DOP is described and shown. SOPs of two extreme points in the main axis are just two PSPs. After one time scrambling, 3500 SOPs are distributed equally in the Poincare sphere. The DOP of all SOPs can be calculated under the condition that splitting ratio is 0.5, with two SOPs at maximum DOP being two PSPs and two SOPs at minimum DOP being the SOP. Since the whole information of first-order PMD vector can be acquired, feed-forward PMD compensation will be feasible and fast.
We experimentally demonstrate a 4×10-Gb/s optical multicast scheme using a semiconductor optical amplifier (SOA)
and a single optical source, which produce a 10-GHz multi-wavelength pulse-trains used as the probe light of the SOA.
The multicast principle is based on the multi-wavelength conversion (MWC) by means of the interaction of both cross
gain modulation (XGM) and transient cross phase modulation (T-XPM) of the SOA. Because of the nonlinear
amplification of SOA, the 4 output copies are regenerated with respect to the input degraded signal. This scheme is very
simple and allows photonic integration.
KEYWORDS: Polarization, Feedback signals, Polarization control, Signal processing, Polarimetry, Detection and tracking algorithms, Beam splitters, Signal detection, Control systems, Optoelectronics
Polarization mode dispersion compensation for fiber communications systems of higher rate is of great importance. Key elements in polarization mode dispersion compensation are polarization controllers and differential group delay lines. Usual ways of compensation for PMD is to control both elements with the same feedback signals, which are processed with an algorithm for control of these elements. Algorithms should be designed for both the controller and delay line with an input signal and give out controlling signals for both elements alternatively. This may cause aimless action of DGD line or polarization state controlling. This paper gives a method of controlling these compensating elements, the polarization controller and the variable differential delay line, with different feedback signals, i.e., to control compensation elements for PMD Compensation separately. It uses Stocks parameters to control polarization controller and uses degree of polarization (DOP) to a variable delay line.
KEYWORDS: Polarization, Digital signal processing, Polarimetry, Telecommunications, Eye, Gaussian pulse, Process control, Optoelectronics, Fiber optic communications, Signal processing
We firstly derive the mathematical expression of degree of polarization (DOP) for Gauss pulse sequence, then analysis theoretically the relationship between DOP and differential group delay (DGD). The relevant experiments well demonstrate the relationship of DOP-DGD. We get the conclusions that the DOP-DGD curve is independent of fibre dispersion, line chip, and bit rate, and are affected by the width of optical spectrum and splitting ratio. Based on the theory, we successfully complete an automatic PMD compensation system for first-order PMD, which can compensate PMD in the optical link in real-time. The response time of compensation system can reach several milliseconds.
Based on the analysis of the MIL-STD-1773 data bus modulation scheme, two optical modulation schemes are proposed for designing this kind of data bus, namely, partial tri-level Manchester II bi-phase coding (PTMBC) and extended Manchester II bi-phase coding with beginning-stopping flags (EMBC-BSF), which can efficiently solve the problem related to three outputs at a MIL-STD-1773 optical receiver with low complexity. Then we focus on the analysis of error probability and optical receiver sensitivity for MIL-STD-1773 data buses with three modulation schemes of Manchester II bi-phase coding, PTMBC , and EMBC-BSF. The results show that both the PTMBC and EMBC-BSF modulation schemes have almost the identical and worse receiver sensitivity than that of the Manchester bi-level coding by ~3dB.
Based on the assumption of a quasi-monochromatic wave for light in fibres and 2□2 coherency matrix, a relationship of DO P with several parameters as well as DGD is derived from the common definition of DOP. A normalized coherent coefficient, showing the degree of correlation of optical signals in both principal states of polarization (PSPs), is derived theoretically. The value of this parameter indicates directly the degree of polarization of optical signals within the communications fibers. The correlation is also the straightforward express of differential group delay between two PSPs. With a pulse shape of Gaussian, we give a useful expression of DOP with power splitting ratio and differential group delay. Two curves of calculations are also given. When DGD becomes bigger, the coherent coefficient is smaller, meaning that the DOP is lower. DOP is one of feedback control signals for dynamic PMD compensation.
We completed a 5-degree of freedom PMD compensator with a novel feedback control algorithm. The tracking algorithm, which successfully solves the problem of easily been trapped into local optima is adopted in the tracking course with no visible worsening of the feedback signal in the compensation process. Long time testing shows good performance of our compensator for fast tracking and compensation.
In this paper, a novel scheme of stabilizing all-optical clock recovery is proposed, which uses a mode-locked fiber ring to extract the same frequency clock pulses from the uneven multiplexing 4×10Gbps optical signals. The super-mode suppression ratio reaches 60dB (for signals of 10Gbit/s) and an improvement of 20dB is achieved by adding stabilization devices. Wavelength shift is less than 0.01nm within 2 hours, and this value is about one sixties of that without adding stabilization devices. The results show much better cavity length stability and noise suppression performance.
Polarization dependent characteristics of the fiber-optic transmission systems become more important than ever before as the bit rates increase to 10 Gb/s and beyond. We derived the Jones matrix and Muller matrix of a polarization controller (PC), and in our experiment, we can get every wanted state of polarization (SOP) at the PC output with all kinds of input SOP. Using PC as a key component, we designed a polarization stabilizer. With the unknown change of the input SOP and random shift of the environment, the polarization stabilizer can maintain a fixed SOP through controlling the PC in real-time.
Theoretical calculations are made on the basis of relationship between electrical power and differential group delay (DGD). Curves are given representing the change of electrical power with DGD, central frequency of electrical signal and power ratio γ between principal states of polarization (PSPs). Experimental results confirming the theoretical calculations are also presented for voltage V changing with DGD. Factors affecting the feedback signals are proposed and means are given to make the fluctuations smaller. Eye patterns show the effectiveness of a PMD compensation prototype for a 10Gbit/s pseudo random sequence. Receiver sensitivity under 3 different bit error rates are also measured using BER measuring equipment. Comparisons of results under different conditions are also made, confirming the results and deterioration caused by the simulator is well compensated for by using the compensation system.
This paper presents a method of splitting signals from fast and slow axes of polarization maintaining fibers by using a polarization splitter. The new scheme includes a turning connector and a polarization splitter. The polarization splitter will split signals from a fiber and give two separated outputs. It gives some theoretical calculations and the relations between the turning angle and output power from the splitter. It also analyzes the relationship of electrical power spectrum versus differential group delay and relative angles between the axis of a fiber and direction of a polarization splitter. Preliminary experiments are also given in this paper. The scheme has a great potential of becoming an effective method of solving polarization mode dispersion (PMD) problem.
The PMD-induced pulse broadening may cause degradation of receiver sensitivity and has negative effects on the power spectrum of received signals. The paper deals with derivation of the effects of PMD-induced pulse broadening on receiver sensitivity based on the concept of mean square pulse width. It analyzes in detail the effects of PMD on the spectrum of received power. It also discusses the scheme with which the power of a certain frequency component is extracted as a feedback control signal in a PMD compensation system.
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