In January 2011, Laser Focus World reported on a multicrystal scheme for 56% efficient second-harmonic generation (SHG) of near-infrared light at 1064 nm to green light at 532 nm. Now, that same team of researchers from the Institute of Photonic Sciences (ICFO) and the Catalan Institute of Research and Advanced Studies (ICREA), both in Barcelona, Spain, have developed a multicrystal optical parametric oscillator (OPO) that can provide two arbitrary, independently tunable pairs of signal and idler wavelengths.

In conventional OPOs, although the output signal and idler frequencies ω₁ and ω₂ can be varied, they are always linked to one another through energy conservation and phase-matching conditions and cannot be independently tuned. This has been a fundamental limitation of OPOs since they were first demonstrated nearly 50 years ago. The researchers overcame this fundamental limitation using two nonlinear crystals inside a single OPO cavity. Using this new technique, it is possible to produce two frequencies (ω₁, ω₁^') from the two crystals that are almost identical (as close as 0.55 THz). Because the device can provide completely independent tuning of frequency pairs (ω₁, ω₂) and (ω₁^', ω₂^'), it can provide any combination of the four frequencies, and therefore truly arbitrary tuning. Contact Goutam Samanta at gsamanta@prl.res.in.