According to an embodiment of the present invention, an optical parametric oscillator (OPO) (e.g., for a laser transmitting device) includes non-linear optical media, optical beam manipulating elements, and a narrow linewidth filter in the form of a rotatable grating. The grating enables rapid tuning of the oscillator to provide an output beam with a desired wavelength. A pump laser provides a pump laser beam, and the non-linear optical media convert the pump beam into light beams with a signal wavelength and an idler wavelength. The angular positions or orientations of the non-linear optical media relative to a longitudinal propagation axis of the optical parametric oscillator (OPO) are adjustable to effectively tune the resulting signal and idler wavelengths. An output coupler receives the resulting beams from the non-linear optical media, and emits beams with the desired wavelength (signal and/or idler wavelengths).