There are several frequency conversion applications associated with lidar-based remote sensing that would benefit from the use of high-quality, complex (i.e., chirped, multi-section, or otherwise modulated) domain-engineered magnesiumoxide- doped lithium niobate (MgO:LN). While congruently melting lithium niobate (CLN) has been explored in detail over the last decades, it is known to be highly susceptible to photorefractive damage, which has limited the achievable performance of some QPM-assisted (quasi phase matching) structures that are commercially available. The demand for high-performance engineered nonlinear optical (NLO) materials, in terms of power handling, efficiency, conversion bandwidth, and accessible wavelength range, has driven the development of high-quality, large-area wafers of MgO:LN. While commercial outlets for these materials exist, there is still a need to expand the achievable performance of these structures (i.e. larger aperture bulk structures, higher efficiency waveguide structures, and implementation of sophisticated poling designs that increase achievable conversion bandwidths).

Use of bulk and waveguide-based domain-engineered MgO:LN will allow the manufacture of highly efficient and compact wavelength conversion modules for second-harmonic generation (SHG), as well as sum- and difference-frequency generation (SFG/DFG), providing a path to the development of compact, singlefrequency, spectroscopically useful laser sources. In addition, these devices can be configured for broadband and high-gain optical parametric amplification (OPA) in the near-IR spectral region.

During this effort, process steps were developed that will enable the fabrication of high-quality, complex, domain-engineered MgO:LN using both traditional wafer-level poling and AdvRs patented submount poling process. Using these steps, waveguides were fabricated for frequency doubling in the 1550-nm spectral regime achieving normalized conversion efficiencies of up to 30%/W-cm2 and low propagation losses of 0.14 dB/cm at the fundamental wavelength. Several hundred milliwatts of NIR light were generated inside these waveguides at room temperature without the immediate onset of photorefractive damage. For CLN, a twodimensional nonlinear diffusion model enabled researchers to determine the exchange conditions and waveguide geometry required to optimize a targeted QPM waveguide-based interaction. As part of this effort, the initial steps towards a similar model for proton diffusion in MgO:LN were performed.

In addition, an approach to periodic poling of large-aperture (up to 2 mm) MgO:LN for use in pulsed, high-energy, nonlinear frequency conversion was developed using submount poling. Samples with QPM periods as short as 31 μm were prepared in these thick substrates. This poling period will allow OPO-based generation of 1.67-mm pulses, which is of interest for lidar-based remote sensing of methane.

This work was done by AdvR, Inc. under the direction of Philip Battle, and at Stanford University under the direction of Carsten Langrock and Martin Fejer for Goddard Space Flight Center. For further information, contact the Goddard Technology Transfer Office at (301) 286-5810. Refer to GSC-16934-1