Predicting shapes of hysteresis loops on the output of tunable external-cavity semiconductor lasers

Studies have been made of the nonlinear characteristics of grating tuned external-cavity semiconductor lasers with the aid of the analytical expression of the threshold carrier density required for the laser to oscillate at different frequencies. After connecting refractive index with carrier density through the spectral broadening factor and choosing an appropriate reference carrier density, the key points defining hysteresis loops on the N-ν (carrier density-frequency) curves have been determined analytically. Consequently, different shapes of hysteresis loops on P-ν (power-frequency) curves have been predicted. The validity of the theory has been examined using the data provided by different papers