Circular Hole Grating Improves Low Threshold 1650 nm Laser Diode for Gas Detection

An efficient laser methane detection system is highly dependent on the performance of a laser diode (LD) that emits at 1653.7 nm. The LD must have high power, low threshold, and narrow linewidth output characteristics. We have developed an LD design that incorporates a slot waveguide and a circular hole grating structure. This design improves the laser’s output characteristics by increasing the effective area of the electric field and reducing the grating coupling coefficient. A low grating coupling coefficient can achieve low grating loss and narrow spectral linewidth. The LD has a threshold current of 15 mA, which corresponds to a threshold current density of approximately 500 A/cm². The maximum output power is about 20 mW, the spectral linewidth is 10 pm, and the side mode suppression ratio (SMSR) is 32 dB. The device structure is transferred to the wafer surface using a stepper lithography machine, eliminating the need for electron-beam lithography and secondary epitaxy. It effectively reduces the complexity and cost of fabrication. This device has significantly advanced an efficient laser methane detection system.