Mechanism of the noise reduction method by superposition of high-frequency current for semiconductor injection lasers

Semiconductor injection lasers sometimes reveal excess noise called the mode hopping noise, which is associated with the mode hopping phenomena among longitudinal modes. The mode hopping phenomena are caused by coupling effects among lasing modes. To reduce this kind of noise superposition of high-frequency (HF) current on the injection current is frequently used. This reduction method is theoretically analyzed based on the mode competition theory and is compared with experimental measurements. It is confirmed that the coupling effect among the longitudinal modes is released with the HF superposition because of enhanced vibration of the injected electron, resulting in reduction of the mode hopping noise