We report the experimental characterization of mechanically induced long-period fiber gratings (LPFG's) made by pressing a plate with periodic grooves against a short length of fiber. This filter, which is simple and inexpensive, exhibits transmission spectra and temperature stability similar to those of photoinduced LPFG's. It also offers the unique advantages of being tunable, erasable, and reconfigurable. Its polarization dependence also makes it useful as a polarizer, although it can also be eliminated with simple mechanical designs.

EYDFA, L-band superfluorescent outputs of the SFS are greatly increased. So ASE seed source with L-band flat output spectrum is important for this two-stage broadband source.Furthermore, there may be lasing around 1565 nm with low P LD1 , as shown in Figure 6(a), which can be avoided with the increase of the ASE signal of the seed source. Lasing is caused by Rayleigh backscatter in the pumped EYDF. The condition of causing lasing is G␣L (NA) 2 /(4n 2 ) Ͼ 1, where G is the effective mean gain, ␣ is the fiber loss coefficient, L is the fiber length, and NA is the numerical aperture [7]. The G of EYDF is large and easily causes lasing due to the presence of Yb 3ϩ . The ASE signal from the seed source consumes inversive particulates and decreases G so as to avoid lasing. The experimental results show that the lasing can be avoided when the P seed is more than 0.64 mW (with corresponding P LD1 of about 61.1 mW). When the P LD2 of 1.14 W is engaged, minimum P seed for preventing from lasing falls to 0.21 mW (with corresponding P LD1 of about 51.6 mW). Obviously, higher P LD2 leading to larger inversive population requires higher P seed in order to prevent lasing. CONCLUSIONA two-stage high-power L-band SFS has been obtained using a DPF ED ASE seed source with a 980-nm pumped LD amplified by a double-pass Er/Yb co-doped double-cladding fiber amplifier pumped by a 976-nm LD array. A considerable increase of output power is achieved by using the EYDFA. Output power of 216 mW and conversion efficiency of 13.7% are obtained with 77.1-mW seed-source pump power and 1.50-W amplificationstage pump power. The ASE signal of the seed source benefits from the improved output spectrum. And the resonant lasing emerging near the C-band on the output spectra of the SFS can be effectively suppressed with an increase of the seed-source pump power. analysis of microstrip circuits. EFFICIENT ADI-FDTD/MODIFIED MATRIX PENCIL METHOD FOR MICROWAVE INTEGRATED CIRCUIT ANALYSIS

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