Longitudinal modes evolution of a GaN-based blue laser diode

• High resolution spectra of a commercial GaN blue laser diode were studied.
• The laser power and central wavelength were found to have excellent stability.
• The temperature induced shift in the gain was larger than shifts in the modes.
• The measured mode spacing agreed with calculated value.

Spectral emission of a single-transverse Fabry–Perot GaN-based blue laser diode was experimentally investigated to study the evolution of its longitudinal modes. A 0.003-nm resolution spectrometer was employed to detect and record emission spectra of the laser diode in the wavelength range between 440 and 450 nm as a function of the operating current and temperature. The stability of the laser was investigated over continuous 14 h by monitoring variations in emitted power and central wavelength and found to exhibit excellent stability. The longitudinal mode spacing of 0.0548 nm was found to agree with corresponding calculated mode spacing. The longitudinal modes were observed to shift at rates of 0.0045 nm/mA and 0.0154 nm/°C toward longer wavelengths. Similarly, the gain was observed to shift towards longer wavelengths but with a rate of 0.0432 nm/°C.