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121.
A new interference cancellation technique for direct-detection optical code- division multiple-access (OCDMA) network employing
pulse-position modulation (PPM) is proposed in this paper. The multiple access interference (MAI) estimation is achieved by
pre-reserving one of optical spreading code sequences at the receiver based on the correlation property of padded modified
prime codes (PMPC). The estimated interference is then cancelled out after photo-detection process. Additionally, the transmitted
signal is Manchester-coded to further improve the system performance. Based on this proposed interference canceller in a shot-noise
limited regime, we have obtained an expression for the upper bound of the bit-error probability (BEP) taking into account
effects of both MAI and shot-noise. This BEP is compared with that of a PPM-OCDMA without cancellation. Finally, the receiver
structure of the proposed optical network unit (ONU) is fairly simple to compare with the conventional cancellation schemes. 相似文献
122.
介绍了第八届亚洲物理奥林匹克竞赛中实验考题——"干涉法测量玻璃热膨胀系数和折射率温度系数"的内容、实验原理,并对实验的考试结果进行了分析. 相似文献
123.
124.
研究了一种新型模拟双折射结构DWDM滤波器的中心频率和带宽的可调谐特性.研究表明:当给定满足一定平坦化要求的光谱透射率所需的各模拟波片中偏振旋转器的旋转角时,通过模拟波片中楔形介质对的相对位移来调节光在各模拟波片中的光程差,同时保持光程差仍满足特定的比例关系,可实现中心频率及带宽的调谐.当光在各模拟波片中的光程差变化较小时,可实现中心频率的调谐,此时带宽的改变很小,可忽略不计;随着光程差变化的不断增大,带宽的改变则不能忽略. 相似文献
125.
In certain species of moths and butterflies iridescent colors arise from subwavelength diffractive surface corrugation of
the wing-scales. The optical properties of such structures depend strongly on wavelength, incidence angle, and state of polarization
of illuminating radiation, and the viewing angle. In this paper, we study the reflection spectra of the wings of the Morpho didius butterfly by simulating a double-layered model of a transverse cross-section comprised of the ground scale and the cover
scale. Each layer contains a certain quasi-periodic arrangement of tree-like subwavelength microstructures. The simulation
is done using a high accuracy nonstandard finite-difference time-domain (FDTD) method in two dimensions. We assume that the
structure is made of a slightly lossy dielectric material. The wavelength dependence of the complex refractive index for the
ground scale of Morpho didius is assumed to be similar to that of Morpho sulkowskyi. The complex refractive index in the latter case was obtained by comparing the computed reflection/transmission spectra with
corresponding experimental measurements at normal incidence. 相似文献
126.
In this paper we have proposed a novel prime spreading sequence family hereby referred to as “new-Modified Prime Code (n-MPC)”
for direct-detection synchronous optical code-division multiple-access (OCDMA) networks. The new code has been applied to
Overlapping Pulse-Position Modulation (OPPM) CDMA system and the performance of system is evaluated. In addition, we have
analyzed the system throughput and also introduced a new interference cancellation technique which significantly improves
the bit error probability (BEP) of OPPM-OCDMA systems. 相似文献
127.
A parallel plate interferometer with a reflecting mirror for measuring angular displacement is proposed. A deflection angle
of a beam caused by an angular displacement is amplified by use of a reflecting mirror to increase the optical path difference
(OPD) in the plane-parallel plate, which provides high sensitivity of the phase measurement. Detection of light transmitted
through the plane-parallel plate with a position sensitive detector (PSD) enables high accurate measurement of the initial
angle of incidence to the plane-parallel plate with insensitivity to stray light. The improved parallel plate interferometer
achieves a measurement repeatability of 10−8 rad. 相似文献
128.
The real part of the effective index is enhanced in a metal-insulator-metal (MIM) surface plasmon waveguide when the thickness of the insulator is quite small and this mechanism can be utilized to achieve some ultra-compact photonic devices. The mode properties of an index-guided multimode plasmonic waveguide of subwavelength size are analyzed and the multimode interference (MMI) effect is investigated. A novel ultra-compact MMI power splitter, with the transverse size less than 1/3 of the free space wavelength, is proposed. 相似文献
129.
130.
This study proposes a common path interference optical system for the measurement of refractive indices and thickness of uniaxial crystal material. The measurement system comprises an accurate Mach–Zehnder laser interferometer, a single-axis rotary stepping motor, and a computer. The laser interferometer is composed of a single-frequency He–Ne laser, two-beam splitters and two reflectors. The Mach–Zehnder laser interferometer measures the optical length difference by using its linear measurement accuracy. The proposed solution procedure enables both the refractive indices and the thickness of the optical waveplate to be obtained. The proposed design differs from conventional designs in that it does not use a heterodyne modulator with a lock-in technique. It is shown that the refractive indices and thickness of the tested optical elements can be measured rapidly and accurately. 相似文献