Monolithically Integrated Extended Cavity Diode Laser with 32 kHz 3 dB Linewidth Emitting at 1064 nm

Abstract The spectral linewidth of semiconductor lasers is a crucial performance parameter in a growing number of applications. A common method to improve the coherence of the laser relies on increasing the optical cavity length by an extended section without gain material. Here, this extended cavity diode laser (ECDL) concept is realized in a monolithic device at 1064 nm wavelength. This is accomplished by applying a two‐step epitaxy in the aluminum gallium arsenide material system to selectively remove the active layers in a specific section of the chip. The extended passive section decreases the 3 dB linewidth to 32 kHz at 1 ms integration time. A direct comparison between the performance of the monolithic ECDL and a distributed Bragg reflector laser from the same wafer demonstrates the feasibility of the approach. The results in terms of frequency noise, side mode suppression ratio, injection current threshold, and slope efficiency show that the passive section reduces the laser linewidth while the additional interfaces within the laser cavity created by the manufacturing process do not deteriorate the electro‐optical properties or frequency stability. This opens the possibility for the realization of gallium arsenide based photonic integrated circuits by monolithically combining active and low‐loss passive waveguides.