We investigate gain equalization of a four-mode-group and six-mode-group erbium-doped fiber amplifiers with a genetic algorithm for mode division multiplexing transmission systems by optimizing rare earth dopant profile and pump modes powers, respectively. The optimizing gains are calculated to be > 28 dB between 1520 nm – 1565 nm with a maximum differential modal gain of ~ 2 dB among the mode groups only by optimizing the rare earth ring doping profile in the few-mode erbium-doped fiber.
High resolution wavelength-tunable lasers are essential to sensing applications. For sensing applications,
high resolution is needed to improve the spatial resolution and/or measurement accuracy, and fast tuning
(sweeping) is required to enhance the measurement speed for dynamic sensing. However the demand of
high resolution conflicts with the requirement of fast continuous wavelength tuning. The solution to this
issue is tuning the wavelength of the output in a quasi-continuous way in which the length of each step is
dependent on the frequency of a RF generator which is used to drive a single-sideband (SSB) modulator in
the wavelength-swept optical system. In this paper, a principle of the step-tunable wavelength-swept
optical system is proposed and demonstrated. The two optical features of narrow bandwidth and fairly high
optical output power make the system unique for improving the accuracy of the measurement of the
center-wavelength of a fiber Bragg grating (FBG) sensor. In addition, changing the tuning-step by
adjusting the frequency of a RF generator electrically is user-friendly compared to the conventional
wavelength swept systems by tuning optical elements mechanically.