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To form a low noise figure and uniform shortpass band in optical fiber communications an improved automatic filtered power control (AFPC) pumping method is proposed here. A modulated single laser signal was entered in a closed feedback loop, in which the erbium-doped fiber amplifier (EDFA) was used as a part of the AFPC loop. Owing to the constant filtered signal and the quadrature phase shift delay inside the feedback loop, an optical pass band was uniformly formed. This EDFA attains high performance with a low noise figure simultaneously. The method was successfully applied to the fabrication of practical 12.0 m length of erbium-doped fiber pumped at 980 nm wavelength and 20 dBm power. Experiments prove that the signal gain of the loop remain flat in the range of 18.2 to 22.4 dB with a worst case error of ±0.5 dB and the noise figure was reduced by 2.2 dB at optimal, which correspond to a shortpass range of 40 nm band pass from 1525 nm to 1565 nm in wavelength. Of course, it should be possible to extent the system performance to all pumping configurations for semiconductor optical amplifiers. This provides the simplest and most economical way to transmit a well-defined band of modulated laser signal and to reject all other unwanted radiation.

A novel ion concentration in liquid detection measurement method is proposed. This new technique uses an improved low pass filter (LPF) photonic band gap (PBG) cell structure, which is laid out on board a printed circuit (PCB). This paper demonstrates how the method can be applied to measure the concentration of CuSO4 with the advantage of low cost. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 387–389, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11068