The point spread function (PSF) of imaging system with coded mask is generally acquired by practical measure-
ment with calibration light source. As the thermal radiation of coded masks are relatively severe than it is in
visible imaging systems, which buries the modulation effects of the mask pattern, it is difficult to estimate and
evaluate the performance of mask pattern from measured results. To tackle this problem, a model for infrared
imaging systems with masks is presented in this paper. The model is composed with two functional components,
the coded mask imaging with ideal focused lenses and the imperfection imaging with practical lenses. Ignoring
the thermal radiation, the systems PSF can then be represented by a convolution of the diffraction pattern of
mask with the PSF of practical lenses. To evaluate performances of different mask patterns, a set of criterion
are designed according to different imaging and recovery methods. Furthermore, imaging results with inclined
plane waves are analyzed to achieve the variation of PSF within the view field. The influence of mask cell size
is also analyzed to control the diffraction pattern. Numerical results show that mask pattern for direct imaging
systems should have more random structures, while more periodic structures are needed in system with image
reconstruction. By adjusting the combination of random and periodic arrangement, desired diffraction pattern
can be achieved.
A novel rapidly tunable, low loss, low crosstalk, polarization-independent, four-port reconfigurable optical add/drop multiplexer (OADM) is designed in this article. Electrooptic effect is used in two directions on waveguides which are fabricated on a LiNbO3 substrate by Ti diffusion in order to convert the polarization between TE and TM mode at the download or upload wavelength. Particularly, voltages applied along propagation direction are separated and can be well programmed to suppress the sidelobe and drop multiple channels.
The frequency-stabilized laser in 1.5μm region is vital important for high capacity Dense Wavelength Division
Multiplexing (DWDM).The acetylene (C2H2) saturated absorption frequency stabilization can be used to stabilize the
frequency of laser in 1.5μm region. A fiber grating external cavity semiconductor laser diode(ECLD) was designed
according to the method of frequency stabilization, which used step motor to strain the fiber grating to tune the
wavelength, and modulated the power of light by modulating the injecting current. The effect of frequency stabilization
was authenticated by experiment.
The Resilient Packet Ring (RPR), standardized by the IEEE 802.17 work group, is a new topology technology for bidirectional packet-switched metropolitan backbone networks. The key objective of RPR is to achieve high bandwidth utilization, optimum spatial reuse and fairness simultaneously. Fairness algorithm is one of the core technologies of RPR. One major problem is that the bandwidth allocated by the algorithm oscillates tremendously and permanently under unbalanced traffic scenarios. So the challenge is to design a fairness algorithm in the distributed nature. This paper presented a new dynamic bandwidth allocation algorithm and the analytic results show it is effective in reducing the oscillation in RPR with low computational and time complexity.
KEYWORDS: Fiber Bragg gratings, Semiconductor lasers, Control systems, Wavelength tuning, Voltage controlled current source, Fiber lasers, Light emitting diodes, LED displays, Power supplies, Lithium
In this paper,we introduce a novel tunable external-cavity semiconductor laser that simultaneously achieves rapid tuning rate and tuning precision by mechanical control. A stepping motor is applied in the tuning system. By control of the angular displacement of stepping motor, we can modify the centre wavelength of FBG.
KEYWORDS: Control systems, Semiconductor lasers, Microcontrollers, Temperature metrology, Signal detection, Temperature sensors, Light sources, Laser stabilization, Digital electronics, Optical amplifiers
The temperature greatly influences the characteristics of external cavity laser diode (ECLD). The high accurate temperature control of ECLD is one of the pivotal technologies of stable output wavelength. In this paper, the principle and method for high accurate temperature control of ECLD are described. The scheme of bistable temperature control is given, which is combined by the analog circuit with PID control theory and the digital circuit design based on microcontroller, and it is studied and analyzed.
In this paper, the technology of molecule saturation absorption frequency stabilization of the external cavity laser diodes (ECLD) on 1.5μm which is recently researched is discussed, and it can obtain high ratio of precision. The improved scheme of the servo circuit system of the ECLD’s molecule saturation absorption frequency stabilization is investigated in the paper. The peripheral loop servo circuit system is the key of the frequency stabilization control. The original servo system uses a lot of discrete components. Its structure is intricate and the performance is not stable enough. In the paper, the parts of the peripheral closed loop servo are conformed in an FPGA slug. This module can realize the closed loop control functions which are necessary for the frequency stabilization. So, the whole system is not only integrated and minityped, but also can be intelligent controlled; the stabilization is greatly increased, and it enables the accuracy to reach 10-8rad.
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.
In recent years, frequency stabilization technology of the external cavity laser diodes (ECLD) has developed rapidly. In this paper, an embedded system module that is adopted in the frequency stabilization circuit of ECLD is discussed, and an improved circuit of embedded system that is based on ARM core is presented. In this way, the reliability of frequency stabilization circuit system is increased, the power waste is reduced and the structure is simplified.
Frequency stabilization of laser diodes is of vital importance for the exploitation of optical frequency-division multiplexing coherent transmission systems and high-resolution optical measurement application. The research of frequency standard in 1.5μm region becomes one of hot orientations in optical communication area. The molecules absorption frequency stabilization technology of Fibre Bragg Grating external cavity laser diode (FBG ECLD) is studied intensively. To overcome the shortcoming of traditional PID control, self-organized and self-adapted algorithm based on predictive estimate modelling is used. The algorithm adopts indirectness arithmetic, which estimates and improves on the modelling according to a suitable learning speed and gains perfect control effects. The algorithm which is adopted in embedded system can achieve high-resolution frequency stabilization within 5min warm-up without manual work.
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 double-clad fiber laser is a novel one with high-efficiency. It has many advantages such as narrow line width and tunable, good beam quality and compact configuration. It can be widely used in optic communications, optic sensor, optic measurement, etc. In this paper, the principle and experimental results of double-clad Yb3+-doped fiber laser are reported. This kind of laser is pumped by a high power semiconductor laser array and coupled by a set of lens. The laser output of 209mW at 1.0872μm is obtained with a pump threshold of 192mW. The slope efficiency is 49%.
In this paper, Fiber Bragg Grating external cavity semiconductor laser and Blazed grating external cavity semiconductor laser are analyzed in theory. Some experiments on two types of Blazed Grating external cavity laser (Littrow and Littman set-up) are done, and some conclusions are also obtained. Two set-ups are compared in detail; at last the intending application of the laser is prospected.
The microstrip patch antenna is a low-profile low cost robust planar structure. A wide practical range of can be obtain with this type of antenna and, due to the ease of manufacture, is inexpensive compared with other types of operation, low gain, and a potential decrease in radiation efficiency due do surface-wave losses. In this paper, a new type of high directivity PBG patch antenna is proposed. It has been demonstrated that take advantages of both the suppression of surface waves and high directivity.
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