Intracavity frequency conversion: from bow-ties to whispering galleries

Abstract

Providing optical feedback by a resonator enhances the efficiency of nonlinear optical effects, e.g. frequency conversion. The bow-tie cavity is known to be a very successful scheme and it has made its way into the commercial world of second harmonic generation and parametric oscillation. We demonstrate a continuouswave optical parametric oscillator based on a bow-tie cavity converting monochromatic pump light at 1.03 µm wavelength to signal light being tunable from 1.25 to 1.85 µm and to corresponding idler light from 2.3 to 5.3 µm. We observe a signal power of up to 7 W, an idler power up to 3 W, and a mode-hop free operation over 10 h without any active stabilization. Furthermore, we have extended the tuning range of the parametric oscillator to the terahertz region: Our system converts near-infrared pump light to a monochromatic wave with a frequency of 1.35 THz and a power of 2 µW. Now, the straightforward next development step is to reduce the footprint of such devices. For this purpose another type of ring cavity is very promising: the whispering gallery resonator. This system offers unequaled opportunities because of its low loss leading to a high finesse. We discuss the challenges for transferring the parametric oscillation scheme to whispering gallery resonators, addressing the preparation of suitable resonators with a quality factor of 10 7 and a finesse of 500 and locking of the pump laser to a cavity mode for 3 hours.