Multiwavelength Fiber Lasers Based on SOA and Double-pass Mach-Zehnder Interferometer

Using a direct double-pass and an isolator-assisted double-pass waveguide-based Mach-Zehnder interferometer (MZI), we demonstrate high-performance SOA-based multiwavelength fiber ring lasers with respective channel spacing of 21.5 GHz and 43 GHz. By changing the fiber ring cavity loss of direct double-pass MZI based configuration, we show that over one hundred of lasing wavelengths in the C- or L-band spaced at 21.5 GHz can be obtained with a power non-uniformity less than 3 dB and an extinction ratio of 28 dB. Since the direct double-pass MZI configuration degrades the extinction ratio and reduce the free spectral range (FSR) of the MZI to half, an isolator-assisted double-pass MZI configuration is further proposed to enhance the extinction ratio while maintaining the FSR. A stable 55-wavelength simultaneous oscillation spaced at 43 GHz is accordingly achieved in C-band with an extinction ratio of higher than 50 dB. Compared with the 0.058 nm linewidth of each lasing wavelength for the single-pass MZI configuration, narrower linewidths of 0.038 and 0.028 nm are obtained for the isolator-assisted and direct double-pass MZI configurations, respectively.