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51.
Jin Xue Nanxi Li Kan Wu Jia Haur Wong Chunmei Ouyang Sheel Aditya Perry Ping Shum 《Optics Communications》2012,285(2):153-157
This paper investigates the effectiveness of phase noise suppression by incoherent addition in a passively mode-locked fiber laser. Incoherent addition is achieved by using an interferometer external to the mode-locked laser. Two different types of interferometers, Mach–Zehnder and ring, are investigated experimentally for different background phase noise levels. Measurements show that both types of interferometers can achieve good phase noise reduction for a background phase noise level above ? 130 dBc/Hz. Effects of dispersion management and pulse train intensity ratio in the interferometers are also discussed. Multi-stage cascaded interferometers are proposed for supermode noise suppression of harmonically actively mode-locked lasers. 相似文献
52.
In this Letter, we propose general optimization methods to design broadband high-efficiency grating couplers for planar waveguides. We attribute the coupling bandwidth to the mismatch of effective indices between the diffracted beam and the actual grating structure around the operation wavelength for fiber to waveguide excitation. The coupling bandwidth formula is deduced. A simple parameter-separate optimization procedure is proposed for general layered grating couplers for high coupling efficiency. Using our principle, we optimized a grating coupler for a horizontal slot waveguide operating at wavelength 1.55 μm for TM polarization. The grating coupler has 1 dB bandwidth of 60 nm and coupling efficiency of 65% with incident light from single-mode optical fiber (SMF) at 8°. 相似文献
53.
We propose and demonstrate a novel and simple dual-parameter measurement scheme based on a cascaded optical fiber device of long-period grating (LPG) and photonic crystal fiber (PCF) modal interferometer. The temperature and refractive index (RI) can be measured simultaneously by monitoring the spectral characteristics of the device. The implemented sensor shows distinctive spectral sensitivities of -30.82 nm/RIU (refractive index unit) and 47.4 pm/°C by the LPG, and 171.96 nm/RIU and 10.4 pm/°C by the PCF modal interferometer. The simultaneous measurement of the temperature and external RI is experimentally demonstrated by the sensor. The temperature shift and RI shift calculated by the sensor matrix agree well with the actual temperature and RI change in the experiment. 相似文献
54.
We propose a novel fiber Fabry-Perot interferometer (FPI) that incorporates a length of microfiber as its cavity and two fiber Bragg gratings (FBGs) as reflectors. The microfiber FPI is simply fabricated by flame-heated taper-drawing the central spot of an FBG into a section of microfiber. Ambient refractive index (RI) influences the effective index of microfiber, and thus the free spectrum range of the microfiber FPI, resulting in RI sensing. A dual-wavelength fiber laser based on the microfiber FPI is constructed, enabling radio frequency interrogation with high resolution. RI sensitivity of 911 MHz/RIU is experimentally demonstrated for microfiber FPI with equivalent diameter of 1.455 μm. Simulation results indicate that the sensitivity can be further enhanced by reducing the diameter of the microfiber. 相似文献
55.
A normal subgroup N of a finite group G is called an n-decomposable subgroup if N is a union of n distinct conjugacy classes of G. Each finite nonabelian nonperfect group is proved to be isomorphic to Q 12, or Z 2 × A 4, or G = ??a, b, c | a 11 = b 5 = c 2 = 1, b ?1 ab = a 4, c ?1 ac = a ?1, c ?1 bc = b ?1?? if every nontrivial normal subgroup is 2- or 4-decomposable. 相似文献
56.
Polarization mode dispersion (PMD) is the ultimate limitation to high bit-rate fibre communication system. The stability of PMD is very important to its measurement and compensation. This paper puts forward a method to measure the stability of PMD by measuring the stability of the state of polarization (SOP) and introduces the conception of time evolution vector (TEV) of SOP. We observe the fact that the regularity of the principal state of polarization changing with time is the same as other SOPs‘‘, if we neglect the dependence of TEV on wavelength. We also measure the SOP‘‘s stability of some fibres with different lengths, and obtain results of PMD changing with time. 相似文献
57.
We measured macro-bending losses for two large mode area photonic crystal fibers. Experimental results show that macro-bending loss and loss window are dependent on the parameter d/Λ and number of air-holes ring in the cladding. 相似文献
58.
In this paper, it is proved that a finite group G is p-nilpotent if every minimal subgroup of P∩Op(G) is permutable in P and NG(P) is p-nilpotent, and when p=2 either [Ω2(P∩Op(G)),P]Ω1(P∩Op(G)) or P is quaternion-free, where p is a prime dividing the order of G and P is a Sylow p-subgroup of G. By using this result, we may get a series of corollaries for p-nilpotence, which contain some known results. Some other applications of this result are also given. 相似文献
59.
A novel channel allocation method, based on optimal golomb ruler, that allows reduction of FWM effect while maintaining bandwidth efficiency, is presented. Simulation is carried out to show performance improvement in WDM systems without inducing bandwidth increase. 相似文献
60.
Lattices of subgroup and subsystem functors are investigated. In particular, it is proved that for the case where X is a formation
of finite groups and width of the lattice F0(X) is at most |π(X)|, the formation X is metanilpotent and |π(X)| ⩽ 3.
__________
Translated from Algebra i Logika, Vol. 45, No. 6, pp. 710–730, November–December, 2006. 相似文献