Simple Estimation of Fiber Dispersion and Laser Chirp Parameters Using the Downhill Simplex Fitting Algorithm

Abstract

International audienceWe report on a simple and fast method to estimate the fiber dispersion and laser chirp parameters on a dispersive Intensity Modulation and Direct Detection (IM/DD) optical channel. Based on the general IM/DD small-signal frequency response, we use the Downhill-Simplex algorithm to fit the channel measurement retrieved with a network analyzer to a general mathematical model. The method is proven to be quite efficient for light sources of different natures and with different adiabatic and transient chirp characteristics, including a Distributed Feedback (DFB) laser, an Electroabsorption modulator (EAM) and even a Reflective Semiconductor Optical Amplifier with fiber-Bragg grating (RSOA-FBG)

Impact of Chirp in High-Capacity Optical Metro Networks Employing Directly-Modulated VCSELs

“…The frequency of the fading dips depends on the cumulated CD, moving towards lower frequencies for higher dispersion. Moreover, laser chirp parameters have a strong impact on the shape of the frequency-selective channel, modifying the position and the extent of the spectrum dips [10]. Therefore, a complete characterization of the optical source in terms of chirp properties can be achieved by fitting the uncompensated channel transfer function.…”

Beyond 25 Gbit/s Directly Modulated, Directly Detected OFDM Using Channel Flattening by a Fabry-Perot Filter

“…The small-signal frequency-domain analysis is an established technique to evaluate the chirp and dispersion parameters of lasers and fibers [4,6,7]. Even if the small-signal modulation regime is not always representative of large-signal operation of the channel, SSFDA is of a powerful tool allowing a practical frequency-domain analysis of how the many parameters limiting the capacity of the link will interact with each other.…”

“…This will limit even further the maximum allowed bit-rate of the link. This term will also act on the heights of the transmission lobes of the channel due to phase-to-intensity modulation coupling [6,7]. The FM term, which is related to the adiabatic chirp, can nevertheless be beneficial to transmission.…”

“…In order to quantify the filter impact on transmissions, we use the method proposed in [7] to extract the laser chirp parameters from the small-signal channel measurements. The theoretical curves after fitting (dashed lines in Fig.…”

TDM-PON PAM Downstream Transmission for 25 Gbit/s and Beyond

“…Relative Intensity Noise (RIN) is added as an Additive White Gaussian Noise (AWGN). The frequency deviation generated by the chirp is applied following the model depicted in [20]. The 8 GHz cut-off frequency of the photodiode used is lower than the relaxation oscillation frequency of the DFB laser in our experimental setup.…”