Long-term stabilization of single longitudinal mode in external cavity semiconductor lasers

Long-term frequency stabilization of a single longitudinal mode (SLM) external cavity semiconductor laser has been demonstrated by using multisegment composite-cavity configuration and automatic frequency control loop with feedback to control the external cavity length. The time period of mode-hopping free SLM operation has been observed to be more than 24 hours with a frequency shift of about 28 MHz and a linewidth of less than 200 kHz.