In this study, the noise figure (NF) improvement is demonstrated in double-pass C-band erbium-doped fiber amplifier. It is used the short length of unpumped erbium doped fiber (EDF) within a circulator-based loop mirror which is reduced amplified spontaneous emission (ASE). The unpumped EDF attenuates part of the ASE that is then reflected back for a double pass configuration which in turn, helps to improve the gain and NF. The proposed configuration has lower NF and higher gain than conventional double pass scheme. Thus, it can be easily applied for practical application.ABSTRACT: This article presents a new quadrature voltage-controlled oscillator (QVCO). The LC-tank QVCO consists of two first-harmonic injection-locked oscillators (ILOs). The outputs of one ILO are injected to the common nodes of capacitors on the other ILO and vice versa so as to force the two ILOs operate in quadrature. At the supply voltage of 1.1 V, the total power consumption is 5.94 mW. The free-running frequency tuning range is 11.5%, tunable from 6.56 to 7.36 GHz as the tuning voltage is varied from 0.0 to 2 V. The QVCO has been implemented with the TSMC 0.18-lm CMOS technology and the die area is 0.504 3 0.803 mm 2 . The measured phase noise at 1-MHz offset is 2123.01 dBc/Hz at the oscillation frequency of 7.34 GHz and the figure of merit of the proposed QVCO is about 2192.5 dBc/Hz.

In this study, designed and optimized C and L band ErbiumDoped Fiber Amplifiers (EDFA) around 70 nm bandwidth, 36.53 dB average gain with an average noise figure of 5.8 dB properties are used. For this purpose, 16 channels Wavelength Division Multiplexed (WDM) system with channel spacing of 5.3 nm is taken into account. -30 dBm powers at the input signals (1530 nm-1610 nm) are applied to three port filter and then input signals are separated into C and L bands. Each band signals are separately amplified in double pass configuration. Finally, all signals are combined into a coupler and the overall configuration has wide bandwidth, high gain and low noise.

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