Narrow-Linewidth 2128 nm Optical Parametric Oscillator with an External Resonator Based on a Reflective Volume Bragg Grating

In this paper, we report an external-cavity 2128 nm narrow-linewidth optical parametric oscillator involving a reflective volume Bragg grating. Based on the Sellmeier equation, we introduce the thermal expansion coefficient together with the thermally-induced output wavelength shift. When the pump power is 12.91 W, with the repetition rate being 70 kHz, a 2128 nm laser with an output power of 3.85 W is obtained, having the optical-to-optical conversion efficiency equal to 30% and the linewidth equal to 108 nm. Moreover, the output power is 2.71 W at 2128 nm and the output linewidth is compressed to 0.19 nm, when a reflective volume Bragg grating is used instead of a total reflection mirror, with the corresponding optical-to-optical conversion efficiency being 21% and the beam quality factor being M-x(2) = 1.92 and M-y(2) = 1.98. As a result, a 2128 nm narrow-linewidth laser is implemented.