Numerical demonstration of wavelength-insensitive tuning characteristics of ladder-type tunable filter for a widely tunable laser diode

We propose a wavelength-insensitive tunable ladder-type interferometric filter having a novel configuration for use in a widely tunable laser diode. The spectral characteristics of the proposed device are numerically analyzed and compared with those of our previously reported device regarding transmittance and bandwidth. Wavelength-insensitive tuning and flat-topped filter spectra are obtained by optimizing device parameters. We also discuss the applicability of the proposed ladder filter to a widely tunable laser. The proposed tunable laser has a nearly constant threshold current density with tuning current injection. The oscillation frequency of the laser diode can be stabilized by introducing chirping into the ladder filter to obtain a single passband response. These high-performance spectral characteristics make the proposed device feasible for wavelength- division-multiplexing-based systems.