Measurement of gain saturation coefficient of a DFB laser for lasing mode control by orthogonal polarization light

The frequency response of a 1.55-μm distributed feedback (DFB) laser is measured by injecting light which has an orthogonal polarization to the laser´s lasing mode. The injected light, termed as orthogonal polarization light, is carefully selected to not couple to the lasing mode by adjusting its polarization to be orthogonal to that of the lasing mode and by setting its wavelength slightly different from that of the lasing mode. The wavelength of the orthogonal polarization light, however, is set within the range where the laser´s active layer has a gain. The gain saturation coefficients for the lasing light are estimated to be 4.7×10^-23 cm² and that by the injected orthogonal polarization light (almost the same wavelength as the lasing mode) are 3.7×10^-23 cm², respectively