Low-threshold loss-coupled laser diode by new grating fabrication technique

We introduce a novel fabrication method to make InGaAs absorptive first-order grating for loss-coupled distributed feedback laser diode (DFB-LD) using reactive ion etching. By this technique, it is possible to control duty rate of the first-order grating. A very-low-threshold current of 6 mA was obtained from our loss-coupled LD at the wavelength of 1.547 μm, which was unusually high for a loss-coupled LD because of the excessive light absorption. In addition to the low-threshold current, it shows high SMSR and longitudinal single-mode yield as high as 50 dB and 90%, respectively.