Mid-infrared Optical Parametric Oscillators Based On Optical Superlattice

Near-infrared (NIR) and mid-infrared (MIR) lasers are of great interest in laser filed. Optical parametric oscillation is a good way to generate near-infrared (NIR) and mid-infrared (MIR) lasers, with advantage on flexible tunability, high output power, compactness and so on. The technique of quasi-phase-matching (QPM) plays a key role in nonlinear optics. Recently, it is found that cavity phase matching (CPM) is also an effective phase matching method. In this thesis, we demonstrated different kinds of optical parametric oscillators, including continuous wave (CW), nanosecond (ns) and picosecond (ps) optical parametric oscillators. The main content include:1. Firstly, the development of laser and nonlinear optics are introduced. Then, the principle of phase matching technology is elaborated, including birefringence phase matching (BPM), quasi-phase-matching (QPM) and cavity phase matching (CPM). Applications of mid-infrared laser and main methods to generate mid-infrared laser are discussed.2. We elaborated the theory of optical parametric oscillator, including classification of different kinds of optical parametric oscilltors, gain and threshold condition of optical parametric oscillators, wavelength tuning and cavity design methods. Also, the kinds of OPO involved in our experiment were introduced.3. We investigated the continuous wave (CW) intracavity optical parametric oscillator (IOPO), including two types of IOPO:folded intracavity OPO and linear intracavity OPO. In our experiment, we found that, the stability of the linear intracavity OPO is better than the folded intracavity OPO. Besides, the structure of a linear intracavity OPO is simpler, so we developed an engineered linear intracavity OPO. Compared with an extracavity OPO, the intracavity OPO is more compact, and the threshold is lower. In conclusion, an intracavity OPO is suitable for the applications which need mid-infrared laser with low power.4^ The technique of the continuous wave (CW) extracavity OPO was studied. We demonstrated a fiber laser pumped OPO based on MgO.PPLN with multi-periods, from which we got the output wavelength from 1.5μm to 4.3μm. And we developed a well-engineered OPO. A fiber-amplified distributed feedback (DFB) laser is used to pump a continuous wave OPO. Frequency modulation of the DFB laser was transferred to the 3.3μm idler, which was used in the methane gas detection experiment. Also, we developed another engineered OPO according to the experiment.5. We demonstrated a picosecond (ps) synchronously pumped OPO.1.5-4.3μm ps laser output was obtained via a MgO:PPLN crystal with eight grating periods. We designed a cascade OPO-OPA process to increase the power of 3.8μm output. Compared with a single OPO process, the conversion efficiency obtained an enhancement of 71%. We developed an engineered picosecond OPO according to the expimental design and results.6. We demonstrated a sheet optical parametric oscillator (SOPO) based on the principle of CPM, which was fabricated with a type I MgO:LiNbO3 crystal with a thickness of 500μm. Frequency combs were obtained near the degenerate point of 1064nm, with a coverage of 45nm and a mode spacing of 0.5nm. The optical efficiency of the SOPO is up to 23.9%.